20 court cases that changed how the law works

Most laws are written by legislatures, but much of what the law actually means gets decided in courtrooms. A statute or a constitution is only as clear as its most ambiguous clause, and when two parties fight over that ambiguity, a judge has to pick a meaning. The most consequential of those picks do more than resolve one dispute. They set precedents that bind every court below, reshape how governments operate and change how ordinary people live, work, marry, speak and stand trial.

This list gathers 20 cases that did exactly that. Most come from the U.S. Supreme Court, which sits at the center of the world's most heavily litigated constitutional system. Others come from the U.K., India and Australia, and one from an international tribunal, because the common law tradition and modern human rights law are global projects. A snail in a Scottish ginger beer bottle still shapes product liability law from London to Wellington. A land claim by a Torres Strait Islander rewrote property law across an entire continent.

Some of these decisions expanded rights: the right to a lawyer, the right to marry, the right to remain silent. Others restricted them in ways later generations came to regard as grave errors, and those cases matter just as much. Dred Scott and Plessy v. Ferguson are on this list not because they were correct but because they shaped a century of American life and forced the legal system to confront what it takes to undo a precedent. The law changes by accretion and by rupture, and both processes are visible here.

Each entry explains the dispute that started the case, what the court decided and why the ruling still matters. Read together, they trace how courts acquired the power to strike down laws, how that power has been used and abused, and how a single lawsuit — often brought by an ordinary person with no money and long odds — can end up rewriting the rules for everyone.

The case that gave American courts their power began as a squabble over a piece of paper. In the final days of his presidency, John Adams appointed dozens of Federalist judges and justices of the peace. William Marbury was one of them, but his signed commission was never delivered before Thomas Jefferson took office. Jefferson's secretary of state, James Madison, refused to hand it over. Marbury sued directly in the Supreme Court, asking for an order compelling delivery.

Chief Justice John Marshall faced a trap. If the court ordered Madison to deliver the commission, the Jefferson administration would likely ignore it, exposing the court as powerless. If it refused, the court would look like it was capitulating to political pressure.

Marshall found a third path. He ruled that Marbury was entitled to his commission, but that the court could not issue the order, because the statute giving the Supreme Court jurisdiction to hear such cases — a section of the Judiciary Act of 1789 — conflicted with the Constitution. When a statute and the Constitution collide, Marshall wrote, courts must follow the Constitution. The statute was void.

That reasoning established judicial review: the power of courts to strike down laws passed by Congress. The Constitution never grants this power explicitly. Marshall inferred it from the document's structure and from the idea that a written constitution would be meaningless if legislatures could ignore it.

The immediate outcome was minor. Marbury never got his job, and the decision demanded nothing from Jefferson. The long-term consequences were enormous. Judicial review became the foundation of American constitutional law and a model exported around the world. Nearly every major case on this list — from Brown v. Board of Education to Citizens United — depends on the power Marshall claimed in 1803. Courts in dozens of countries now exercise some version of it, making Marbury arguably the most influential single decision any court has issued.

Two questions sat at the heart of this case: Could Congress charter a national bank, and could a state tax it? The answers defined the balance of power between the federal government and the states for the next two centuries.

Congress chartered the Second Bank of the United States in 1816. The bank was unpopular, particularly in states whose local banks resented the competition. Maryland responded with a tax on any bank operating in the state without a state charter — a measure aimed squarely at the national bank's Baltimore branch. James McCulloch, the branch cashier, refused to pay, and the dispute went to the Supreme Court.

Chief Justice John Marshall's opinion answered the first question with a broad reading of the Necessary and Proper Clause. The Constitution never mentions a bank, but it grants Congress powers to tax, borrow, and regulate commerce. Marshall reasoned that Congress may choose any appropriate means to carry out its enumerated powers, so long as the means are not prohibited. A national bank was a legitimate tool for managing federal finances, so the charter was constitutional.

On the second question, Marshall held that Maryland's tax was invalid. A state tax on a federal institution would let a single state undermine an instrument created for the whole nation. The power to tax, he reasoned, carries the power to weaken or destroy, and no state may wield that power against the federal government. Federal law, under the Supremacy Clause, prevails over conflicting state action.

McCulloch gave the federal government room to grow. The doctrine of implied powers underpins much of what Washington does today, from the Federal Reserve to federal criminal law to social insurance programs. Every fight over the reach of congressional power — including modern battles over health care mandates and environmental regulation — still runs through the framework Marshall built in 1819.

No decision in American history is more widely condemned, and few did more damage. Dred Scott was an enslaved man who had lived for years with his enslaver in Illinois, a free state, and in the Wisconsin Territory, where the Missouri Compromise banned slavery. After returning to Missouri, Scott sued for his freedom, arguing that residence on free soil had made him free.

The Supreme Court, led by Chief Justice Roger Taney, ruled against him in sweeping terms. Taney held that Black Americans, whether enslaved or free, could not be citizens of the U.S. and therefore had no right to sue in federal court. He went further, declaring the Missouri Compromise unconstitutional on the ground that Congress lacked the power to ban slavery in the territories, because doing so deprived enslavers of property without due process.

The decision was meant to settle the slavery question. It did the opposite. It enraged the North, energized the new Republican Party, deepened the sectional crisis and helped propel the country toward civil war. Abraham Lincoln attacked the ruling repeatedly in his debates with Stephen Douglas, arguing that it rested on false history and a corrupted reading of the founding documents.

Dred Scott was never formally overruled by the court. It was overturned by constitutional amendment. The 13th Amendment abolished slavery in 1865, and the 14th Amendment in 1868 wrote birthright citizenship into the Constitution, directly repudiating Taney's holding.

The case changed how the law works in two lasting ways. It demonstrated that the Supreme Court could inflict catastrophic harm when it reached beyond the dispute before it to impose a political settlement. And it established the pattern by which the gravest judicial errors get corrected: not by the court itself, but by amendment, war and generational political struggle. No later court cites it as authority for anything except what to avoid.

Homer Plessy boarded a whites-only railroad car in Louisiana in 1892 as a deliberate act of civil disobedience. Plessy, who was one-eighth Black under Louisiana's racial classifications, was recruited by a New Orleans civil rights committee to challenge the state's Separate Car Act of 1890, which required railroads to provide separate accommodations for Black and white passengers. He was arrested, as planned, and his case reached the Supreme Court.

The court upheld the law by a 7-1 vote. The majority reasoned that the 14th Amendment guaranteed legal equality but did not require social integration, and that segregation did not by itself stamp Black citizens with a badge of inferiority. If segregation felt degrading, the majority suggested, that was a matter of perception rather than law. The decision blessed the formula that came to be known as separate but equal.

Justice John Marshall Harlan dissented alone. He argued that the Constitution recognizes no racial castes among citizens and that the law must treat all citizens the same regardless of color. His dissent became one of the most cited in American history and supplied the intellectual foundation for the legal attack on segregation decades later.

Plessy's practical effect was to give constitutional cover to Jim Crow. States across the South segregated schools, transit, parks, hospitals, courtrooms and cemeteries, and the equal half of separate but equal was never enforced. Black schools and facilities received a fraction of the funding of white ones, and courts looked away.

The decision stood for 58 years until Brown v. Board of Education dismantled it in public education. Plessy's legacy is a warning about how courts can launder injustice into doctrine — and a demonstration that a lone dissent, written in defeat, can eventually supply the reasoning that wins. Louisiana pardoned Homer Plessy posthumously in 2022, 130 years after his arrest.

The most influential case in the history of tort law began with a bottle of ginger beer in a café in Paisley, Scotland. May Donoghue's friend bought her a drink in August 1928. The bottle was opaque, and after Donoghue had consumed some of its contents, the remains of a decomposed snail allegedly poured out with the rest. She said she became ill, and she sued the manufacturer, David Stevenson.

The legal obstacle was contract. Donoghue had not bought the drink herself, so she had no contract with the café or the manufacturer. Under the law as it then stood, a manufacturer generally owed duties only to the party who purchased the product. A consumer injured by a defective product she had not personally bought often had no one to sue.

The House of Lords, then the U.K.'s highest court, changed that. Lord Atkin's leading judgment held that a manufacturer owes a duty of care to the ultimate consumer of its products when the goods reach the consumer in the form they left the factory, with no reasonable opportunity for intermediate inspection. He grounded the duty in what became known as the neighbour principle: a person must take reasonable care to avoid acts or omissions that could foreseeably injure people closely and directly affected by their conduct.

That principle became the foundation of the modern law of negligence across the common law world, including the U.K., Canada, Australia, New Zealand and much of the Commonwealth. It also paralleled and reinforced developments in American product liability law.

Nearly every negligence claim today — against a carmaker, a hospital, a builder, a software firm — descends from the framework the case established. Whether the snail actually existed was never proven; the case settled before trial on the facts. The principle it produced outlived the dispute entirely.

Linda Brown was a third-grader in Topeka, Kansas, who had to travel to a distant Black school when a white school stood blocks from her home. Her father joined a lawsuit organized by the NAACP, which had spent decades building a litigation strategy against segregation. The Supreme Court consolidated the Kansas case with challenges from South Carolina, Virginia, Delaware and Washington, D.C., and heard argument from Thurgood Marshall, who would later join the court himself.

The question was whether racially segregated public schools could ever satisfy the 14th Amendment's guarantee of equal protection. Under Plessy v. Ferguson, states had answered yes for more than half a century, so long as facilities were nominally equal.

Chief Justice Earl Warren delivered a unanimous opinion holding that separate educational facilities are inherently unequal. The court reasoned that segregating children by race generates a sense of inferiority that damages their education and development, regardless of whether the buildings and books match. In public education, the court concluded, the doctrine of separate but equal has no place.

The ruling did not desegregate schools by itself. A follow-up decision in 1955, known as Brown II, ordered compliance with deliberate speed, a phrase that Southern states exploited to delay for years. Massive resistance, school closures and federal-state confrontations followed, including the 1957 crisis in Little Rock, Arkansas, where federal troops escorted Black students into Central High School.

Brown changed how the law works in a deeper way than any single desegregation order. It showed that the Supreme Court would overturn entrenched precedent when the precedent was rotten, and it made the court a central battleground for social change. The civil rights litigation model it validated — patient, strategic, incremental — became the template for movements on behalf of women, disabled people, immigrants and LGBTQ Americans seeking change through the courts.

Cleveland police arrived at Dollree Mapp's home in 1957 looking for a bombing suspect and gambling equipment. She demanded a warrant. Officers eventually forced their way in, waved a piece of paper they claimed was a warrant — it was never produced at trial — and searched the house. They found no suspect, but they found allegedly obscene materials, and Ohio prosecuted Mapp for possessing them.

Since 1914, federal courts had followed the exclusionary rule: evidence obtained through an unconstitutional search could not be used in a federal prosecution. But the rule did not bind the states, and roughly half of them admitted illegally seized evidence in their own courts. A defendant's Fourth Amendment rights could be violated with impunity as long as the prosecution was local.

The Supreme Court used Mapp's case to close that gap. It held that the exclusionary rule applies to state prosecutions through the 14th Amendment. Without the rule, the court reasoned, the constitutional ban on unreasonable searches and seizures would be an empty promise, because police would face no practical consequence for ignoring it. Excluding tainted evidence removes the incentive to violate the Constitution in the first place.

The decision transformed American policing. Departments had to train officers on warrant requirements, probable cause and the limits of searches, because sloppy work could sink a prosecution. Suppression hearings became a routine feature of criminal cases, and an enormous body of Fourth Amendment doctrine grew up around questions of what counts as a search and when exceptions apply.

Critics have argued ever since that the rule lets guilty people go free on technicalities, and later courts carved out exceptions, including a good-faith exception for officers who reasonably rely on defective warrants. The core principle survives: in an American courtroom, how the police found the evidence matters as much as what they found.

Clarence Earl Gideon was charged with breaking into a pool hall in Panama City, Florida, in 1961. He was too poor to hire a lawyer and asked the trial judge to appoint one. The judge refused, because Florida law provided appointed counsel only in capital cases. Gideon defended himself, lost and received a five-year sentence.

From his prison cell, Gideon mailed a handwritten petition to the Supreme Court, arguing that the Constitution entitled him to a lawyer. The court agreed to hear the case — it appointed the prominent attorney Abe Fortas, a future justice, to argue for him — and used it to answer a question it had gotten wrong two decades earlier. In 1942, the court had held that states need not provide counsel to poor defendants in most felony cases.

The court overruled that precedent unanimously. The Sixth Amendment's guarantee of counsel, it held, is fundamental to a fair trial and applies to the states through the 14th Amendment. Lawyers in criminal courts are necessities, not luxuries, the court reasoned; governments spend heavily on prosecutors, and defendants who can afford it hire the best lawyers they can, which shows that legal representation is essential rather than optional.

Gideon was retried in Florida, this time with an appointed lawyer, and a jury acquitted him.

The decision created the modern public defender system. Every state had to build machinery for providing counsel to indigent defendants, and later rulings extended the right to misdemeanor cases carrying jail time. The promise remains unevenly kept — public defender offices in many states carry crushing caseloads with thin budgets — but the principle is settled. A person facing the loss of liberty in a U.S. courtroom cannot be forced to face the state alone, and one prisoner's pencil-written petition put that rule in place.

In 1960, the New York Times ran a full-page advertisement titled "Heed Their Rising Voices," soliciting donations for the civil rights movement. The ad described police actions against protesters in Montgomery, Alabama, and it contained several factual errors — minor details about song lyrics, arrest counts and police conduct. L.B. Sullivan, a Montgomery city commissioner who supervised the police, sued the newspaper for libel even though the ad never named him. An Alabama jury awarded him $500,000, and the state's courts affirmed.

The case was one of several libel suits that Southern officials were using to punish national news coverage of the civil rights movement. If the verdicts stood, the financial risk of reporting from the South could have silenced the press.

The Supreme Court reversed unanimously. It held that the First Amendment limits how far states can go in awarding libel damages to public officials. Debate on public issues, the court reasoned, should be uninhibited, robust and wide open, and it will inevitably include some error. Requiring critics of government to guarantee the truth of every factual assertion would produce self-censorship.

The court therefore created the actual malice standard: a public official cannot recover for defamation about official conduct unless the statement was made with knowledge that it was false or with reckless disregard for the truth. Later cases extended the standard to public figures generally.

Sullivan rewrote the relationship between the press and power in the U.S. It gave journalists breathing room to investigate officials without fearing ruinous verdicts over honest mistakes, and it underwrote decades of aggressive reporting, from Watergate onward. The standard remains contested — some judges and politicians have called for revisiting it — but it still governs, and it makes American defamation law far more protective of speech than that of the U.K. or most other democracies.

Ernesto Miranda was arrested in Phoenix in 1963 in connection with a kidnapping and rape. After two hours of police interrogation, he signed a written confession. No one had told him that he could remain silent or that he could have a lawyer present. His confession was used at trial, and he was convicted.

The Supreme Court reversed, and in doing so it wrote one of the few judicial opinions that ordinary people can recite from memory. Chief Justice Earl Warren's majority opinion held that custodial interrogation is inherently coercive, drawing on police training manuals that taught officers to isolate suspects and wear down resistance. To protect the Fifth Amendment right against self-incrimination, the court required a set of warnings before questioning: a suspect must be told of the right to remain silent, that statements can be used against them, and that they have the right to a lawyer, appointed free of charge if they cannot pay.

Statements obtained without the warnings, or after a suspect invokes those rights, are generally inadmissible. The decision was 5-4, and dissenters warned it would handcuff law enforcement.

The predicted collapse of confessions never happened. Police adapted, the warnings became a routine script and decades of television cop shows made the Miranda rights a global cultural export. People in countries with no such rule can recite it because they have heard it on American screens.

Miranda changed how the law works by moving constitutional protection from the courtroom into the police station, at the moment when rights are most at risk. It also showed courts acting almost like regulators, prescribing concrete procedures rather than abstract standards. The Supreme Court reaffirmed the decision in 2000, holding that the warnings had become embedded in the fabric of American law. Miranda himself was retried without the confession, convicted on other evidence and later killed in a bar fight.

Richard Loving, a white man, and Mildred Jeter, a Black and Native American woman, married in Washington, D.C., in 1958 and returned home to Caroline County, Virginia. Weeks later, police entered their bedroom at night and arrested them. Virginia's Racial Integrity Act of 1924 made interracial marriage a felony, and the couple's out-of-state wedding was no defense. They pleaded guilty and received a suspended one-year sentence on the condition that they leave Virginia for 25 years.

The Lovings moved to Washington, D.C., but wanted to go home. In 1963, Mildred wrote to Attorney General Robert F. Kennedy, who referred her to the American Civil Liberties Union. The resulting case reached the Supreme Court in 1967, when 16 states still banned interracial marriage.

The court struck down the bans unanimously. Chief Justice Earl Warren's opinion held that Virginia's law violated the 14th Amendment twice over. It denied equal protection, because it rested on racial classifications designed to preserve white supremacy — the state punished interracial marriage only when one partner was white. And it denied due process, because marriage is a basic civil right, and the freedom to marry a person of another race resides with the individual, not the state.

The decision erased anti-miscegenation laws that had existed in America since the colonial era. Its influence extends well beyond race. By describing marriage as a fundamental freedom protected by due process, Loving supplied a cornerstone for later cases about intimate life, including the 2015 decision recognizing same-sex marriage, which quoted and relied on it.

Mildred Loving lived quietly in Virginia until her death in 2008. In 2007, on the ruling's 40th anniversary, she issued a public statement supporting the freedom of same-sex couples to marry — a rare instance of a landmark case's plaintiff publicly endorsing its next chapter. The couple's story later reached wide audiences through documentaries and a 2016 feature film.

In December 1965, a group of Des Moines, Iowa, students planned to wear black armbands to school to mourn the dead in Vietnam and support a truce. School officials learned of the plan and preemptively banned armbands. Mary Beth Tinker, a 13-year-old junior high student, her brother John and their friend Christopher Eckhardt wore them anyway and were suspended.

Their families sued, and the case reached the Supreme Court. The question was whether public school students have First Amendment rights while in school, and if so, how far those rights extend.

The court ruled 7-2 for the students. Neither students nor teachers, the majority held, shed their constitutional rights to freedom of speech or expression at the schoolhouse gate. The armbands were silent, passive expression — closer to pure speech than to disruptive conduct — and school officials could not point to evidence that they had interfered with schoolwork or discipline. Fear of controversy, or a preference for avoiding uncomfortable topics, is not enough to justify censorship.

The decision announced what became known as the Tinker test: schools may restrict student expression only when they can reasonably forecast that it will cause substantial disruption of school activities or invade the rights of others.

Tinker established that constitutional rights follow people into government-run institutions, a principle with implications far beyond schools. It also opened a half-century of litigation over its limits. Later decisions gave schools more control over lewd speech, school-sponsored publications and speech promoting drug use, and a 2021 case addressed how far school authority reaches into off-campus social media posts.

Mary Beth Tinker became a nurse and, later in life, a free-speech advocate who tours schools talking about student rights. The armband she wore is a fixture of constitutional law casebooks, a reminder that a 13-year-old's protest can define the boundaries of state power.

Few decisions have shaped American law and politics as thoroughly as Roe — first by existing for 49 years, then by being erased. The case began when Norma McCorvey, identified in court papers as Jane Roe, challenged a Texas law that banned abortion except to save the mother's life.

The Supreme Court ruled 7-2 in her favor. Justice Harry Blackmun's opinion located a right to abortion in the constitutional right to privacy, which earlier cases had grounded in the 14th Amendment's due process clause. The court balanced that right against state interests using a trimester framework: minimal regulation in the first trimester, regulation to protect maternal health in the second, and permissible bans after fetal viability in the third, with exceptions for the mother's life and health.

The decision invalidated abortion bans in the majority of states and became the axis around which American judicial politics rotated. Confirmation hearings, presidential campaigns and state legislative sessions were fought in its shadow for two generations. In 1992, Planned Parenthood v. Casey preserved what it called Roe's essential holding while discarding the trimester framework in favor of an undue burden standard, allowing more state regulation.

In 2022, Dobbs v. Jackson Women's Health Organization overruled both cases. The court held 5-4 on that question that the Constitution confers no right to abortion, returning the issue to the states. Within months, abortion was banned or severely restricted in roughly a third of the country while other states expanded protections.

Roe's rise and fall changed how the law works in ways that transcend the abortion debate. It demonstrated the reach of unenumerated rights doctrine, then demonstrated that no precedent is permanent. The overruling reopened questions long thought settled about how much weight precedent carries, and it reshaped public understanding of what a change in the Supreme Court's membership can do.

The Watergate scandal produced the definitive ruling on whether a president is above the law. During the investigation into the 1972 break-in at Democratic National Committee headquarters, it emerged that President Richard Nixon had taped his Oval Office conversations. Special prosecutor Leon Jaworski subpoenaed the tapes for use in the criminal trial of Nixon's former aides. Nixon refused to comply, asserting executive privilege — the president's claimed right to keep internal communications confidential.

The case moved to the Supreme Court at extraordinary speed, and the stakes were plain. If the president could unilaterally withhold evidence from a criminal proceeding, no investigation could ever reach the White House.

The court ruled against Nixon 8-0, in an opinion by Chief Justice Warren Burger, whom Nixon had appointed. The court recognized, for the first time, that executive privilege exists and has constitutional roots: presidents need candid advice, and candor requires some confidentiality. But the privilege is not absolute. A generalized claim of confidentiality, unconnected to military or diplomatic secrets, must yield to the specific need for evidence in a criminal trial. The judiciary, not the president, decides where that line falls.

Nixon complied. The tapes included the June 23, 1972, recording known as the smoking gun, which captured Nixon approving a plan to obstruct the FBI's investigation. His remaining congressional support collapsed, and he resigned 16 days after the decision — the only U.S. president to do so.

The ruling established two principles that continue to structure fights between presidents and investigators. Executive privilege is real, which presidents of both parties have invoked ever since. And it has limits that courts enforce, which is why subpoena battles involving presidents, from the 1990s through the Trump era, have ended up before judges rather than being settled by presidential fiat. The case remains the standard citation for the proposition that no person, including the president, stands above the law.

The most important case in Indian constitutional history began with a monastery's land. Kesavananda Bharati, the head of a Hindu religious institution in Kerala, challenged state land reform laws that restricted the management of the monastery's property. The case grew into a confrontation over a far larger question: Could India's Parliament amend the constitution without limit, even to the point of abolishing fundamental rights?

The government argued yes. The constitution's amendment provision contained no express limits, and Parliament, as the voice of the people, should be supreme. Opponents argued that unlimited amendment power would let a temporary majority dismantle democracy itself — repeal elections, courts or rights — while claiming to follow the constitution's own procedures.

A 13-judge bench, the largest in the Supreme Court of India's history, heard the case over months and split 7-6. The majority crafted a compromise known as the basic structure doctrine. Parliament may amend any provision of the constitution, but it may not alter or destroy the constitution's basic structure. Judges have since identified elements of that structure to include democracy, secularism, federalism, judicial review and the rule of law, though the list has never been closed.

The doctrine was tested within years. During the Emergency of 1975 to 1977, when Prime Minister Indira Gandhi suspended civil liberties, the court used the basic structure doctrine to strike down a constitutional amendment that sought to place her election beyond judicial scrutiny.

Kesavananda changed how the law works far beyond India. Courts in Bangladesh, Pakistan, Kenya and elsewhere have adopted versions of the basic structure doctrine, and constitutional scholars worldwide treat it as the leading answer to a hard question: how a legal system protects itself from being legally destroyed. It stands for the idea that some constitutional foundations lie beyond the reach of any majority.

For two centuries, Australian law rested on a fiction: that the continent was terra nullius, land belonging to no one, when British colonization began in 1788. Under that doctrine, Indigenous Australians held no legal rights to the lands their peoples had occupied for tens of thousands of years.

Eddie Koiki Mabo, a Meriam man from the island of Mer in the Torres Strait, set out to destroy the fiction. Working as a gardener at James Cook University in the 1970s, he learned from academics that, in the law's eyes, his family did not own the land it had cultivated for generations. In 1982, he and four other Meriam plaintiffs sued Queensland, asserting that their people's traditional ownership had survived colonization.

The litigation took a decade. Queensland even passed a law attempting to extinguish the claim retroactively, which the High Court of Australia struck down in an earlier phase of the case. In June 1992, the High Court ruled 6-1 for the plaintiffs. It rejected terra nullius as a legal foundation and held that native title — rights to land arising from traditional laws and customs — survived the Crown's acquisition of sovereignty, except where governments had validly extinguished it, as by granting freehold to settlers.

Mabo never saw the victory. He died of cancer in January 1992, five months before the judgment.

The decision forced a reconstruction of Australian property law. Parliament passed the Native Title Act in 1993 to create a system for recognizing claims, and native title has since been recognized over large portions of the continent, particularly in the north and west. Beyond land, Mabo changed the country's account of itself: the law now acknowledges that Australia was occupied, not empty, when the colonists arrived. Few single judgments have rewritten both a nation's property system and its founding story.

Jim Obergefell married John Arthur on an airport tarmac in Maryland in 2013 because Arthur, dying of ALS, could not travel farther from their home in Ohio, which did not recognize same-sex marriages. When Arthur died, Ohio refused to list Obergefell as his surviving spouse on the death certificate. Obergefell sued, and his case was consolidated with challenges from Michigan, Kentucky and Tennessee.

The Supreme Court ruled 5-4 that the 14th Amendment requires every state to license marriages between two people of the same sex and to recognize such marriages performed elsewhere. Justice Anthony Kennedy's majority opinion rested on both due process and equal protection. Marriage, the court held, is a fundamental right — a conclusion built on precedents including Loving v. Virginia — and the reasons it is fundamental apply with equal force to same-sex couples: individual autonomy, the importance of a two-person union, the protection of children and families, and marriage's role as a keystone of social order.

The four dissenters argued that the Constitution says nothing about marriage and that the question belonged to voters and legislatures, warning that the court was short-circuiting democratic debate.

The ruling extended marriage equality to the entire U.S. at a stroke. Same-sex couples gained more than a thousand federal rights and responsibilities tied to marriage, covering taxes, immigration, inheritance, medical decisions and military benefits. It arrived after a rapid legal and cultural shift: a dozen years earlier, no U.S. state permitted same-sex marriage.

Obergefell also illustrates how constitutional change compounds. It drew on Loving's account of marriage as a fundamental right and on a line of gay rights precedents Kennedy himself had written since 1996. In 2022, Congress added a statutory backstop, the Respect for Marriage Act, requiring federal and interstate recognition of same-sex marriages regardless of what future courts might decide.

The case that reshaped American campaign finance began with a movie. Citizens United, a conservative nonprofit corporation, produced "Hillary: The Movie," a film critical of Hillary Clinton, and wanted to distribute it through video-on-demand during the 2008 primary season. Federal campaign finance law barred corporations and unions from spending general treasury funds on electioneering communications close to elections. The nonprofit sued the Federal Election Commission.

The Supreme Court could have decided the case narrowly. Instead, it ordered reargument on a broader question and ruled 5-4 that the government may not restrict independent political spending by corporations and unions at all. Justice Anthony Kennedy's majority opinion held that political speech does not lose First Amendment protection because the speaker is a corporation, and that independent expenditures — spending not coordinated with a candidate — do not give rise to corruption or its appearance in the constitutional sense. The decision overruled two precedents and struck down a central provision of the 2002 McCain-Feingold campaign finance law.

The dissent, read from the bench by Justice John Paul Stevens, ran 90 pages and argued that corporations are not people for political purposes and that the ruling would unleash a flood of money into elections.

Combined with a lower court decision the same year, Citizens United enabled the creation of super PACs: committees that may raise and spend unlimited sums on independent political advocacy, provided they do not coordinate with campaigns. Billions of dollars have since flowed through them, along with politically active nonprofits that do not disclose their donors.

The ruling changed how the law works by making corporate political speech a constitutional right and by narrowing the definition of corruption that can justify regulation. It remains among the most publicly contested Supreme Court decisions of the century, with repeated calls for a constitutional amendment to undo it.

A shipwreck and an act of cannibalism produced one of the criminal law's foundational rulings on necessity. In 1884, the English yacht Mignonette sank in a storm in the South Atlantic, leaving four crew members adrift in a small lifeboat with almost no food or water. After roughly three weeks, with the youngest member of the crew — a 17-year-old cabin boy named Richard Parker — comatose from drinking seawater, Captain Tom Dudley and mate Edwin Stephens killed him. The three survivors, including a third man who did not participate in the killing, fed on the body until a passing ship rescued them days later.

Back in England, Dudley and Stephens spoke openly about what had happened, expecting the protection of what sailors regarded as an accepted, if grim, custom of the sea. Instead, they were prosecuted for murder. Their defense was necessity: killing one person had been the only way to save three lives.

The court rejected the defense. The judgment held that necessity is no defense to murder. The law cannot permit a person to decide that another's life is worth less than their own, the court reasoned, and it asked who could be qualified to choose which innocent person must die. Allowing such a defense would make legal principle bend to temptation precisely when the temptation is strongest.

Dudley and Stephens were convicted and sentenced to death, and the Crown promptly commuted the sentences to six months' imprisonment — a resolution that affirmed the principle while tempering its application.

The case remains a fixture of first-year criminal law courses across the common law world. It marks the boundary between excuse and license, and it anchors modern debates about torture, triage and trolley problems. The rule it announced still governs: however desperate the circumstances, English law does not permit the deliberate killing of an innocent person to save others.

The International Military Tribunal at Nuremberg was not a single case in the ordinary sense but a founding event: the moment international law acquired the power to hold individuals criminally responsible for atrocities committed by states.

After Germany's defeat in World War II, the U.S., U.K., Soviet Union and France established a tribunal to try the surviving leadership of the Nazi regime. The indictment charged crimes against peace, war crimes, crimes against humanity and conspiracy. Twenty-four men were indicted; 22 were ultimately tried, among them Hermann Göring, Rudolf Hess and Albert Speer. The tribunal convicted 19, sentenced 12 to death and acquitted three. Robert H. Jackson, a sitting U.S. Supreme Court justice, served as chief American prosecutor and framed the trial as reason's answer to vengeance.

Two principles established at Nuremberg transformed the law. First, individuals — including heads of state, ministers and generals — can be criminally responsible under international law. Sovereignty is not a shield, and official position is not a defense. Second, obedience to orders does not excuse participation in atrocity. A soldier or official who carries out a criminal order remains answerable for it, though orders may mitigate punishment.

The trials drew criticism at the time as victors' justice applying retroactive law, and the objections have been debated ever since. But the framework endured. The Nuremberg principles were affirmed by the United Nations, and the category of crimes against humanity entered the permanent vocabulary of international law.

The lineage runs directly to the present. The tribunals for the former Yugoslavia and Rwanda in the 1990s, and the International Criminal Court created by the 1998 Rome Statute, all descend from Nuremberg. Every modern prosecution of a warlord or head of state for atrocities rests on the proposition first enforced in a Bavarian courtroom: that some crimes are so grave the whole world has jurisdiction over them.