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

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

The NATO constitution is intentionally vague about what exactly is required from its members. Explore the historical debates and learn more about common misconceptions about NATO’s common defense clause.

NATO has only invoked its mutual defense clause once, in the days after the 9/11 attacks.

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

NATO was formed in 1949 to deter Soviet expansion, prevent European militarism, and encourage political integration.

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.

NATO's Article 5 has been invoked once—after 9/11

The article was invoked the day after the attacks and launched a series of NATO campaigns to fight global terrorism. This page includes excerpts from a speech by then-NATO Secretary General Jens Stoltenberg about the attacks and the organization’s response.

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.

As of 2025, every NATO member spent at least 2% of GDP on defense, a target the alliance had been pushing toward for over a decade.

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.

NATO consists of 32 countries across North America and Europe.

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.

The threat of nuclear annihilation reshaped global diplomacy

The first use of atomic weapons introduced the possibility of a war with no survivors. This article examines how nuclear fear shaped Cold War diplomacy and continues to influence international relations today.

Experts argue that nuclear war is more likely than is commonly believed

The podcast highlights that many of the world's roughly 12,000 nuclear weapons—capable of triggering global collapse and nuclear winter—remain on high alert. Experts warn that this status, combined with limited public awareness, makes nuclear war disturbingly plausible.

The president has the sole authority to call for a nuclear strike

Under current US policy, the president alone can order the use of atomic weapons at any time without requiring prior approval from Congress—a power rooted in the president's role as commander in chief.

NATO leads cyber war games in Estonia

Estonia is host to one of the world’s largest annual interactive cybersecurity drills. Russia is always considered the main threat, but this year, the war in Ukraine has only added to the stakes.

A primer on the president's nuclear football

During the Cold War, the United States and the USSR were forced to prepare for a nuclear strike at a moment's notice, leading to a new innovation: the so-called "football" (known as the chemodanchik in Russia), a bag containing nuclear strike plans, authentication codes, and likely a communication device, which attended the country's leader wherever they went. This easy-to-read piece breaks down the history and lore around the high-stakes quirk in nuclear governance.

Four Cold War hawks warn: Nuclear weapons still threaten the world

Despite the Cold War's end, the US and Russia still hold 95% of the world's nuclear weapons—many on hair-trigger alert. In this 2010 documentary, top former officials urge urgent action to reduce and eliminate the threat.

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.

A 1983 NATO war simulation provoked the Soviets to prepare for war

The "SNAFU" podcast, hosted by actor and comedian Ed Helms, explores some of the biggest blunders in history. Season one focuses on the 1983 NATO Able Archer military exercise, a war game that simulated nuclear attacks on the Soviet Union. The USSR mistook the exercise for a genuine threat and prepared its forces for war. Helms recounts this almost catastrophic event in world history with his signature humor.

Chernobyl pushed the world to create rapid-alert systems for nuclear accidents

In the aftermath of the disaster, nations adopted new agreements requiring immediate international notification of nuclear accidents. They coordinated emergency assistance—efforts led by the International Atomic Energy Agency to prevent future disasters from being concealed when radiation emergencies occur.

Nearly 90% of the world's 12,187 nuclear warheads are held by Russia and the United States.

The Non‑Proliferation Treaty was designed to prevent new states from developing nuclear bombs

The Treaty on the Non‑Proliferation of Nuclear Weapons (created in 1968, effective 1970) binds non-nuclear states to forgo nuclear weapons and commits nuclear powers to share peaceful technology and pursue disarmament—forming the core of the global non-proliferation regime.

A 'nuclear football' briefcase always accompanies the president

The "nuclear football," carried by a military aide to the president at all times, contains communication equipment that allows the president to order a nuclear strike from anywhere in the world. The president carries "the biscuit," a plastic card containing the launch codes, which are changed daily.

See how global nuclear arsenals surged—then shrank—by country since 1945

Worldwide nuclear stockpiles peaked at over 60,000 warheads in the mid‑1980s during the US-Soviet arms race. Today, about nine nations collectively maintain roughly 12,000 warheads, with Russia and the US still holding the majority.

Germany is pursuing its most significant military buildup since WWII.

The global nuclear arms regime has slowly eroded over the past few decades

Both Russia and the United States have withdrawn from key Cold War-era arms-control pacts. Russia's 2022 invasion of Ukraine marked a turning point, as it suspended its participation in inspections and data-sharing agreements.

The North Korean nuclear threat, explained

What would happen if North Korea gets a working ICBM Watch this six-minute video by Vox for an explanation of the North Korean nuclear threat. The Soviet Union first gave nuclear technology to North Korea in the 1950s, when they helped their ally...

Nuclear weapons in WWII

This 14-minute interactive documentary broaches the subject of the human cost of nuclear warfare. Comparing the number of deaths during World War II with the projected deaths of a nuclear exchange, the video can be paused to delve deeper into individual statistics, historical tidbits, and more data that shows the terrible price humanity would pay.

Visualizing the chemistry of nuclear weapons

Nuclear weapons have devastating effects, but the science of how they work is atomically small. There are two main types of nuclear reaction: fission and fusion. The fission bomb produces immense energy by splitting an atom, the result of firing a...

The 1955 Warsaw Pact was the Soviet Union’s answer to NATO

The pact included Albania, Bulgaria, Czechoslovakia, East Germany, Hungary, Poland, Romania, and the USSR. The pact established collective security and a joint military command between the member countries.

Nuclear-powered missiles replace chemical combustion with energy from nuclear fission

In these systems, energy is added to an airstream, which passes through a nozzle to generate thrust. Because the amount of energy released per unit mass of nuclear fuel is millions of times larger than that of chemical propellants, nuclear missiles can travel faster and farther with less fuel.

Finland and Sweden joined NATO after Russia's invasion of Ukraine

In response to Russia's 2022 invasion of Ukraine, Finland and Sweden abandoned decades of military neutrality to join NATO, marking a major shift in Europe's security landscape and expanding the alliance to Russia's borders.

Ukraine once had the third-largest nuclear arsenal—and gave them all up by 1996.

While both are nuclear weapons, atomic bombs release nuclear energy by splitting large atomic nuclei, whereas hydrogen bombs derive most of their energy from fusing heavy hydrogen isotopes.

An overview of North Korea’s military capabilities

With one of the world’s largest conventional military forces, North Korea is often perceived as a security threat. This multimedia backgrounder by CFR breaks down North Korea’s military capabilities. North Korea has the world’s...

Some scientists propose AI-powered satellites to monitor nuclear weapons in place of arms control treaties

With the New START treaty expired, researchers at the Federation of American Scientists have proposed using satellites and AI to remotely verify nuclear arsenals—replacing the onsite inspections that once built trust between the US and Russia during the Cold War.

A list of reasons against dropping the bomb on Japan

One of the perennial moral debates, the dropping of nuclear bombs on Japanese cities prompted strong, polarizing reactions at the time. This article breaks down one side of the argument: that the bomb was designed for defense, using it was illegal and racist, and that there were alternatives.

A deep dive on the weapons being used by both sides

From ballistic missiles to armed drones, Russia’s invasion of Ukraine is proving the devastating power of modern weaponry. This infographic illustrates and explains the uses and effects of the weapons of choice for both sides of the conflict. Tactics are also explored in regards to their efficacy and consequences, with expert commentary added.

China doubled its nuclear stockpile between 2020 and 2025, with plans for further expansion.

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.

The Soviet Union had a similar sphere of influence policy during the Cold War—the Brezhnev Doctrine

Articulated in 1968, the Brezhnev Doctrine claimed the Soviet Union's right to intervene militarily in its satellite states to prevent any deviation from communist rule. It was used to justify the invasion of Czechoslovakia that same year and the invasion of Afghanistan in 1979.

The origin of atmospheric science while testing nuclear weapons during the Cold War

The arms race between the US and the Soviet Union saw both countries stockpiling and detonating hundreds of bombs underground, underwater, and in the atmosphere. To better predict where nuclear fallout would travel after these tests, scientists developed models that would serve as a foundation for those used to explain atmospheric circulation.

Wartime conferences exposed cracks in the US–Soviet alliance

At the Tehran, Yalta and Potsdam Conferences, Allied leaders coordinated WWII strategy—but deep disagreements over postwar Europe foreshadowed the Cold War. The USSR’s push for influence in Eastern Europe clashed with US and British calls for self-determination.

Watch the historic treaty signing that established NATO in 1949

NATO was created with the signing of the North Atlantic Treaty on April 4, 1949, in Washington, DC. The clip embedded in the webpage includes a newsreel with an excerpt from US President Harry Truman’s speech celebrating the historic day.

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.

NUKEMAP lets you model the effects of a nuclear detonation anywhere on Earth

The tool was built by Alex Wellerstein, a historian of nuclear technology at the Stevens Institute of Technology in New Jersey. NUKEMAP uses declassified weapons data to calculate blast radius, thermal radiation, fallout patterns, and estimated casualties for any nuclear device dropped on any city. More than 50 million people have used it since its 2012 launch.

Bill Nye believes a World War II-level mobilization is needed to end climate change

As part of his science advocacy efforts, Nye has argued that existing technologies, including electric vehicles and renewable energy, can already significantly reduce emissions. However, switching to these technologies requires a more expansive awareness of the problem and a greater sociopolitical willingness by policymakers and the general public.

The Cold War (1947-1991) prompted the birth of NATO and the Soviet Warsaw Pact

The geopolitical rivalry between the United States and Soviet Union was considered “cold" because the two countries never directly engaged in military combat during the time period. This page from the Kennedy Presidential Library outlines the causes and major events of the early Cold War.

An explanation of the weak nuclear force, which can induce some forms of radioactive decay

While the strong nuclear force holds the protons and neutrons together in an atomic nucleus, despite the electromagnetic force pushing protons apart, the weak nuclear force can change the identity, or flavor, of the quarks that make up these particles. In doing so, protons can be converted into neutrons, and vice versa, altering the stability of atomic nuclei.

North Korea, in nine infographics

In recent decades, North Korea has spent nearly a third of its annual Gross Domestic Product on military spending, although data is not always forthcoming. This spending has funded major nuclear and missile projects as a means to deter attacks from...