Members decide to what extent they respond to an attack on an ally

The treaty's Article 5 requires mutual defense, but not necessarily military action

Article 5 of the North Atlantic Treaty established NATO’s principle of collective defense. This resource examines the historical context, legal interpretations, and practical applications of this commitment, including its sole invocation after the Sept. 11 attacks.

How NATO responded to 9/11

The collective defense clause of the NATO constitution has only been invoked one time: after the 9/11 terrorist attacks against the United States. This video explores the immediate actions NATO took to respond to the attacks to support the United States. These firsthand clips from 2001 give a sense of the magnitude of the moment and the difficult decisions facing NATO leaders at the time.

The alliance operates under a "flexible response" doctrine—that is, proportionality

NATO countries' main deterrent against aggression is their ability to respond with nuclear weapons. This video from "The Infographics Show" outlines the purpose of this nuclear arsenal, NATO’s strategy to prevent attacks, and its plans in the event of escalation toward nuclear war.

How NATO works

NATO now includes 32 member nations—but how does the alliance actually function? This explainer breaks down its structure, decision-making process, and funding model. From its founding in 1949 to its collective response after 9/11, here’s how NATO operates on a global scale.

Decisions at NATO are by consensus and must be unanimous

There are two strategic commands in NATO: one in Europe (Supreme Allied Headquarters Command Europe) and another in Norfolk, Virginia (Allied Command Transformation). The alliance is headed by both a military officer and a civilian leader.

NATO was formed in 1949 to deter Soviet expansion and integrate Europe

Europe was in shambles after World War II, which saw 36 million Europeans killed, and the Soviets were looking to increase their influence. Beyond deterring the Soviets, the alliance sought to restore Europe and prevent nationalist militarism akin to the German Nazis and Italian Fascists.

Tensions between the US and European NATO allies

The Associated Press article discusses US Defense Secretary Pete Hegseth's assertion in February of 2025 that restoring Ukraine's prewar borders or NATO membership for the country are both unrealistic. This represented a large rift between the United States and its other NATO allies, prompting concern about America’s commitment to the future of the alliance.

NATO condemned Russia's 2022 invasion of Ukraine

While Ukraine is not a member, NATO responded forcefully to the Russian invasion of the country in 2022. This page from the NATO website offers answers to frequently asked questions about NATO’s response to the invasion, specifically on how NATO is aiding Ukraine.

Poland spends the most on NATO (as a share of GDP) at 4.1%, as of 2024

BBC explores how much each NATO member spends on defense and includes a helpful map displaying the defense spending of European countries as a percentage of GDP.

Questions about the US' commitment to its allies may have sparked a new nuclear age

Some US allies—from Warsaw to Seoul—are reevaluating their security amid doubts over American nuclear commitment, signaling the possibility they may want to acquire their own weapons.

A legal scholar argues that the existing war powers framework may collapse in the event of a major power conflict

The legal tests presidents have used to avoid seeking congressional authorization were designed for weaker adversaries. This piece argues that those tests fail against similarly armed competitors, where even limited strikes risk significant escalation, potentially triggering a constitutional crisis over who has the authority to respond.

The 1941 Atlantic Charter was a World War II alliance and model for the UN

The Atlantic Charter was a pivotal 1941 agreement between Franklin D. Roosevelt and Winston Churchill, outlining shared goals for a post-World War II world rooted in freedom and self-determination. These ideals later inspired the founding principles of the United Nations.

The National Security Council advises the president on foreign policy and national defense

Created in 1947, the NSC coordinates military, diplomatic, and intelligence policy matters. Chaired by the president, it includes key Cabinet officials and senior advisers who shape American responses to global crises and security threats.

In the 1930s, Congress nearly passed a constitutional amendment requiring a national vote before declaring war

The Ludlow Amendment, proposed amid rising isolationism after World War I, would have required a national referendum before Congress could declare war, except in cases of direct attack. It was defeated 209 to 188 in 1938 after Roosevelt lobbied against it.

Nearly half of the discretionary funding in the US is allocated to national defense

The US accounts for roughly 35% of global military spending, with defense taking up nearly half of discretionary funds. In this discussion, Michael E. O'Hanlon of the Brookings Institution explains why these levels are so high—and how they compare historically.

Defiance is choosing to act in line with your values under pressure

Compliance often arises from insinuation anxiety and social pressure, making defiance critical in protecting personal integrity and, in turn, strengthening institutions. Practicing defiance may be achieved through the Defiance Compass framework and can lead to a more values-driven society.

Relationships between countries have become more peaceful since the rules-based order was established

Our World in Data monitors bilateral relationships on a spectrum from open rivalry to "positive peace"—deep cooperation and mutual protection. In 1945, no countries had highly cooperative security relationships. Today, nearly a fifth do.

Debating the Constitution today

The Constitution continues to shape our political and social life today. If you want to understand how today’s political debates connect to the Constitution, check out this podcast from the National Constitution Center. The weekly program features experts from diverse perspectives and explores how constitutional principles shape modern issues.

The US Constitution is widely regarded as the longest-standing written national constitution still in force—see how it has influenced rights worldwide.

Spartans could be both brave and cowardly, contrary to popular belief

Though the militant city-state of ancient Sparta had its fair share of heroic warriors, it wasn't all glorious battle. Contrary to depictions in films like "300," the city-state consisted of land-owning aristocrats not so willing to die for their peninsular polis.

The Arab League has 22 members and very little enforcement power

It was founded in Cairo in 1945 and spans 22 nations across the Middle East and North Africa, ostensibly to coordinate policy on economics, culture, and defense. Its charter says any resolution only binds states that voted for them, rendering most of them toothless.

How to prepare for cyberattacks

An easy-to-digest checklist on the many ways you want protect yourself from a cyberattack before it happens, if it happens, and after it happens.

Reactions inside the House chamber during the State of the Union are highly choreographed

Applause, silence, and coordinated standing—or refusal to stand—are deliberate signals during the State of the Union, used by lawmakers to broadcast allegiance or dissent. At the same time, military leaders and Supreme Court justices largely avoid reacting to preserve institutional neutrality.

The US protects free speech more broadly than any other democracy

Well-known First Amendment lawyer Floyd Abrams explains that the US offers stronger free-speech protections than even close democratic allies, where hate speech is criminalized, libel laws favor plaintiffs, and a "right to be forgotten" can erase truthful information from the internet.

Assessing the effectiveness of peacekeeping forces

This podcast episode of Diplomatic Immunity from Georgetown’s Institute for the Study of Diplomacy explores the evolution of UN peacekeeping over its 70-year history. The podcast is joined by Dr. Lise Howard to examine the origins, challenges, and shifting role of peacekeepers—those “blue helmets” deployed where few others will go—in a broader conversation about multilateralism and global conflict response.

Delegates at the First Continental Congress affirmed loyalty to Britain while protesting

Delegates met in Philadelphia in 1774 to debate how to respond to British acts clamping down on trade and increasing taxes. The result of the congress was to call for the formation of colonial militias and to embargo British goods. Delegates also adopted the Declaration of Rights and Grievances, though there was broad disagreement about how to respond to Britain’s policies.

Explore an interactive map of battles from the American Revolution, along with detailed summaries of each engagement

The Russia-Ukraine conflict is the largest ground war in Europe since World War II in casualties, forces mobilized, and displacement of civilians.

While atoms are normally made of protons, neutrons, and electrons, exotic ones have been built with antimatter—alternate versions of normal matter that live for fractions of a second and are about a billion times as rare.

The idea for the Federal Reserve was conceived in secret in 1910—with bankers donning duck hunt gear for disguise while traveling to a remote country club on Georgia's Jekyll Island

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.

A 2019 Facebook event called on attendees to "Storm Area 51, They Can't Stop All of Us," resulting in countless memes, the creation of a music festival, and eventually the arrests of those who did try to approach the area.

20,000 letters to the advice columnist 'Dear Abby' provide insight into prevailing sex, religion, and LGBTQ fears, anxieties, and concerns from the 1950s onward.

Doctors differentiate between a phobia and fear by asking patients whether their fear interferes with their day-to-day activities.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

Researchers believe the brain consolidates memories, processes emotions, and plans for the future during dream states

Famed poet TS Eliot rejected the manuscript for George Orwell's political fable 'Animal Farm,' writing that its criticism of authoritarianism was not 'the right point of view.'

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.

Larger animals like giraffes, elephants, and blue whales have developed a unique defense against cancer, a phenomenon known as Peto's Paradox

The identity of the Tank Man in the iconic photo from the 1989 Tiananmen Square protests remains unknown and was possibly killed.

In 1984, Operation Smash Hit intentionally crashed a 239-ton train into a nuclear waste canister at 100 miles per hour to prove the canister's safety, which remained completely intact and lost just 0.29 of its 100 pounds of pressure.

Brandi Chastain, the star of the 1999 US victory over China in the 1999 Women's World Cup, was a last-second choice to take the penalty kick that sealed the victory.

In 2025, four executives from large tech companies were given positions in the US Army Reserves—including Palantir Chief Technology Officer Shyam Sankar, which reinforced Palantir's ties with the US military and its role as a leading defense partner.

Visualize how CRISPR-Cas9—a type of immune system used by single-celled organisms to attack invasive viruses—targets and makes precise changes to a gene's DNA.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

Discover the catastrophic consequences of a failure of the US electrical grid—something that is more likely than many Americans think.

The first steps to rebuilding your credit score include getting to know exactly what's on your credit report and figuring out how far you are from the '700 club,' or 'good score' range.

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

Prince's sexually explicit 1984 track 'Darling Nikki' attracted the ire of the Parents Music Resource Center, an advocacy group that inspired the Parental Advisory sticker, even though the song ends with a Christian message.