The US and Denmark signed a military agreement over Greenland in 1951.

The US tried to buy Greenland in 1867 and again after World War II.

During the Cold War, a mid-air fire led to a nuclear bomber crash in Greenland that left a piece of a hydrogen bomb missing to this day.

The US handed control of the canal back to Panama in 1999

This was the result of two treaties signed during President Jimmy Carter's presidency, one shifting control to Panama and the other declaring the canal zone neutral. In recent years, US officials have suggested the US may retake control. Experts agree that the only viable way would be through military force.

The US and Denmark are the only two countries known to abide by a predetermined borrowing limit.

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.

Before World War II, the US was a Pacific power

Decades before Pearl Harbor, the US held major Pacific territories—Hawaii, the Philippines, Guam, American Samoa, and numerous island bases—giving it strategic reach across the western Pacific. This presence increasingly overlapped with Japan’s imperial ambitions in the region, contributing to rising tensions.

Explore over a century of US-Canadian relations.

Most of the world's land-based glacial ice and the planet's only two ice sheets are located in Greenland and Antarctica.

Germany is pursuing its most significant military buildup since WWII.

The National Archives protects billions of historical documents, including the Declaration of Independence and the US Constitution.

This "60 Minutes" segment takes viewers behind the scenes at the National Archives, showcasing how experts use conservation science, security, and technology to preserve cornerstone records—such as the original Declaration of Independence—for future generations.

The Atlantic Ocean is home to the world's largest waterfall—the Denmark Strait cataract—which is more than three times the height of the largest land-based waterfall.

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.

The Panama Canal boosted the US as a world power in trade, engineering, and finance

The effort proved the US could achieve grand engineering projects while granting it influence over (and benefitting economically from) a major interoceanic channel and its host country, Panama.

Explore a map of data centers worldwide, numbering over 12,250 as of August 2026, with over 4,500 in the US.

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.

America’s founding documents were once housed in other government buildings

Today, the Constitution and Declaration are displayed at the National Archives. Still, for more than a century, they were kept by other federal institutions—including the State Department and the Library of Congress—before gaining a permanent home in the 1930s.

The US and South Korea have a robust, if delicate, alliance

The deep ties between South Korea and the United States go back decades, but the relationship hasn’t always been frictionless. When two off-duty American servicemen accidentally killed two South Korean middle-school girls in 2002, it set off anti-American protests that led South Korea to seek a more balanced relationship. The Council on Foreign Relations traces key moments in the two countries’ seven-decade history.

Before Pearl Harbor, the US was a nonbelligerent ally to the Allied powers

Between September 1940 and December 7, 1941, the United States remained officially neutral—yet President Roosevelt incrementally shifted policy from “cash‑and‑carry” to Lend‑Lease, funneling critical military aid to Britain and other allies without entering the war.

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

As of 2025, the US and Qatar dominate global helium production

The US's 42.6% share includes helium imported from Canada and refined within the states. Geopolitical conflicts can cause supply disruptions that impact several advanced technologies, including semiconductor manufacturing, aerospace systems, and medical imaging.

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.

The British Royal Navy—not the US military—enforced the Monroe Doctrine for most of the 19th century

In the early to mid-1800s, the US lacked the ships and military power to prevent European nations from colonizing the Americas. Britain enforced this to protect its commercial interests by keeping rival European powers out of Latin America.

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

Israel is the largest cumulative recipient of US foreign assistance since World War II.

President Trump invoked the Monroe Doctrine in 2025, announcing a new 'Trump Corollary'

On Dec. 2, 2025, the 202nd anniversary of the doctrine, President Donald Trump issued a proclamation reaffirming US "dominance" in the Western Hemisphere. His administration's national security strategy officially codified the "Trump Corollary," stating that the US would prevent non-hemispheric powers from gaining strategic influence in the Americas.

The 1783 peace treaty with Britain formally ended the Revolutionary War and nearly doubled the size of the United States.

A US project proposed a 10-gigaton nuclear bomb capable of global devastation

Planned in the early 1950s by US scientists, Project Sundial aimed to create a 10-gigaton thermonuclear bomb—hundreds of times more powerful than any weapon ever built. Had it been tested, it was expected to cause global environmental catastrophe.

The Nazis and Soviets agreed to a non‑aggression pact in 1939

On August 23, 1939, Nazi Germany and the Soviet Union signed the Molotov–Ribbentrop Pact—a public commitment to not attack each other combined with a secret agreement dividing Eastern Europe into spheres of influence. This pact enabled Germany to invade Poland unopposed from the east and delayed conflict with the USSR until June 1941.

The US once had a plan to nuke the moon

In the 1950s, the US considered detonating a hydrogen bomb on the moon as part of a Cold War show of force. Known as Project A119, the classified plan aimed to create a visible explosion from Earth to signal American dominance in the space race.

The US finished what the French had started with Panama's canal

For about two decades, Suez Canal-builder and Frenchman Ferdinand de Lesseps led the project, but financial troubles forced it into the hands of the US, who completed it in 1914. This timeline, made to accompany the definitive PBS American Experience documentary about the canal, highlights major moments in its construction.

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.

When German submarines lurked in US coastal waters

During World War II, German submarines (also known as U-boats) prowled the Southern coast of the US in 1942 and 1943, sinking more than 60 ships and killing 600 Allied soldiers. The campaign is less well-known, since the major battles in Stalingrad and Midway happened at the time. Several of these submarines and the ships they sank are now popular diving spots.

The US has carried debt since 1791.

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.

View a ranking of the countries with the largest helium reserves, led by the US

Estimated at 20.6 billion cubic meters (727.5 billion cubic feet) as of 2022, US helium reserves are more than double those of Qatar, the second nation on the list. Leading the world in natural gas production, from which helium is recovered, the US also leads global helium production, which helps mitigate shortages resulting from overseas geopolitical tensions.

The US once had a plan to nuke the moon

In the 1950s, the US considered detonating a hydrogen bomb on the moon as part of a Cold War show of force. Known as Project A119, the classified plan aimed to create a visible explosion from Earth to signal American dominance in the Space Race.

The US framework of government has influenced the constitutions of many other countries

In 1787, the US Constitution introduced a system built on the separation of powers and individual liberties, including freedom of speech and religion. Though widely influential, its rigidity has made it less of a modern model as countries adopt more adaptable constitutional frameworks.

The US debt ceiling is the threshold Congress sets for federal borrowing.

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

The Truman Doctrine marked the start of US containment strategy

Introduced in 1947, the Truman Doctrine pledged US support for nations resisting communism—starting with Greece and Turkey—and launched the containment policy that defined early Cold War strategy.

The Berlin Airlift was the largest in history and a major Cold War victory for the US

In 1948, the USSR blockaded West Berlin to pressure America and its allies. In response, the US and its partners launched the largest airlift in history—delivering supplies daily for nearly a year until Stalin backed down.

The United States is the world's oldest continuously operating federal system under a written constitution

The US pioneered federalism in the late 18th century, and many countries later adopted federal systems to manage conflict and share power. This resource features interactive maps that trace the spread of federal systems worldwide from 1900 to the present.

Fort Knox was originally built to be a secure facility for the US Treasury's gold reserves back when the US still operated under the gold standard, a system in which a country's currency is pegged to, and can be converted into, a fixed amount of gold.

The US never formally declared war in Vietnam

Instead of formally declaring war, Congress passed the Gulf of Tonkin Resolution in 1964, granting President Johnson broad authority to use military force. The resolution became the legal basis for escalating US involvement without an official declaration of war.

US defense spending peaked during the Korean War at 13% of GDP

In 1953, during the Korean War, US defense spending reached 13.58% of GDP—more than three times today’s level. That peak marked the most militarized moment of the Cold War, and spending has never returned to that level since.

The global economy runs on US dollars, with nearly 90% of international trade in 2019 being processed in US dollars.

The US dollar became the world's reserve currency, backed by gold, after 44 nations gathered in Bretton Woods, New Hampshire, in 1944 with the intention of rebuilding the global economy.

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.

During the Cold War and into the 21st century, US and Soviet/Russian leaders repeatedly agreed to arms control treaties, though strained tensions have led to the expiration of agreements in recent years.