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

European leaders pursued appeasement of Hitler in the 1930s

In the 1930s, Britain sought to maintain peace by ceding territory to Nazi Germany, most notably via the 1938 Munich Agreement allowing Germany to annex the Sudetenland. These concessions, seen as pragmatic amid anti‑war sentiment, ultimately failed to curb Hitler’s aggression and directly contributed to the outbreak of World War II.

Germany’s invasion of Poland in 1939 launched World War II

On September 1, 1939, Nazi Germany launched a surprise invasion of Poland using blitzkrieg—coordinated air bombardments and armored assaults—to overwhelm Polish defenses within weeks. This lightning-strike strategy shocked the world and signaled both the start of World War II and a revolutionary shift in modern military tactics.

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.

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.

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.

Roosevelt formally recognized the Soviet Union in 1933

In 1933, President Franklin D. Roosevelt formally recognized the Soviet Union—ending 16 years of nonrecognition and aiming to improve trade and stabilize relations amid growing global instability.

Stalingrad was the turning point of WWII in Eastern Europe

The six-month siege (July 1942–February 1943) ended when the Soviet Union’s counteroffensive, Operation Uranus, encircled and destroyed Germany’s 6th Army. This decisive victory shifted momentum permanently to the Soviets on the Eastern Front, marking a major strategic reversal in Europe and undermining Nazi Germany’s war capacity.

The “Phoney War” was an eight‑month build-up to war

From September 1939 to May 1940, following their war declaration on Germany, Britain and France entered a phase of military inaction—even as civil defence measures, naval blockades, and rationing intensified at home. Skirmishes were limited, but the decisive fighting didn't begin until Germany invaded Norway and France in April–May 1940, abruptly ending the uneasy stalemate.

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.

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.

Spies working on the Manhattan Project propelled the Soviet bomb program

Soviet infiltration—most notably by Klaus Fuchs—smuggled detailed implosion-design and hydrogen‑bomb data from Los Alamos to Moscow, cutting the USSR’s development time by at least a year and enabling their first atomic test in August 1949.

The Nazi Party was founded in Germany in 1920 and tried a failed coup in 1923

Founded in Germany in February 1920, the National Socialist German Workers’ Party (Nazi Party) attempted its first major power grab in 1923 with the Beer Hall Putsch—a failed coup in Munich that killed about 16 Nazis and four police officers, led to Hitler’s arrest and treason trial, but ultimately elevated his public profile.

The treaty that ended the First World War laid the groundwork for the Second

On June 28, 1919, the Treaty of Versailles officially ended World War I by demanding severe reparations, territorial losses, military restrictions, and the infamous “war guilt clause” against Germany. However, its harsh terms fostered deep resentment, economic instability, and political turmoil—ultimately becoming a catalyst for World War II.

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.

The origins of Putin's 'Nazism' claim in Ukraine

Ukraine has had a varied history, and is home to a rich diversity of ethnicities, religions, and people. In the time leading up to Russia's attacks on the country, Russian President Vladimir Putin referred to Ukraine as a "Nazi nation", owing to Ukrainian nationalists' acceptance of the invading Nazis as liberators from the Soviet Union in WWII. The history is more complex than that. Read this Smithsonian Magazine article to learn more.

The bizarre 1920 proposal to form a pizza-shaped central European state

In light of the challenges of the Treaty of Versailles, which concluded the Great War, a mostly unknown author, and son of the map's printer, PA Maas suggested central Europe be integrated into a single state. With a central capital in Vienna, 24 Kantons, or regions, would radiate outward in pie-slice shapes.

All‑female Soviet 'Night Witches' terrorized German lines with stealth bombing raids

Flying obsolete Polikarpov Po‑2 biplanes, the all-female 588th Night Bomber Regiment—dubbed “Night Witches” by terrified German troops—flew over 30,000 night missions, dropping 3,000 tons of bombs under near silence.

Nazi Germany replaced Advent calendars with depictions of family life under Nazi rule

During World War II, the Nazi regime banned printed Advent calendars because of religious messaging. Officials instead produced state-approved versions featuring swastikas, tanks, and Nazi symbols.

The WWII passport forgers who saved thousands of Jewish lives

Amid the chaos of Hitler's authoritarian Europe in World War II, Polish diplomats based in Switzerland used the classic toolkit of thieves to help free thousands of Jews: they perfected the art of forgery, faking passports secretly donated by sympathetic Latin American countries. Read the incredible tale of heroism here.

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.

The space race ended with a handshake in orbit in 1975

On July 17, 1975, American and Soviet astronauts docked their spacecraft during the Apollo–Soyuz mission, symbolically ending the space race and marking the first joint spaceflight between Cold War rivals.

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.

The wall separating East and West Berlin was a highly visible symbol of the Cold War

Built in 1961, the Berlin Wall physically separated East and West Berlin for nearly three decades—preventing East Germans from fleeing to the West. Its fall in 1989 signaled the collapse of communist regimes across Eastern Europe.

The modern Olympic truce originated in a real pause in ancient conflict

Back in Ancient Greece, neighboring city-states were constantly at war. So when the Olympics started in 776 BCE, they needed a way to keep the peace. This video from the International Olympic Committee discusses the origins of the Olympic Truce and its reinstatement at the 1994 Games in Lillehammer.

Jean-Paul Sartre worked on 'Being and Nothingness' while a prisoner of war

The Nazis invaded France in May 1940. Sartre, as a member of the French Army, was taken prisoner that June. While he was in captivity, he studied Martin Heidegger and worked on "Being and Nothingness," one of his most famous philosophical works.

Before humans, the Soviet Union and the United States sent animals—including apes, dogs, and cats—to space during the Space Race.

In 1915, workers recovered a submarine-like vessel from the Chicago River, prompting fears of German espionage

American dance legend Martha Graham, sometimes called 'the Picasso of dance,' refused to perform at the 1936 Olympics in Berlin and conceived the piece 'Chronicle' in response to the experience.

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

Volcanic activity may have triggered the Black Death by spewing gases that led to crop failures in Europe, thus forcing the import of grain ships with plague-infested fleas.

The United States has had a tumultuous relationship with Cuba since its 1959 revolution, highlighted by a nuclear crisis and a decades-long trade embargo.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

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.'

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.

In 1945, Surrealist artist Salvador Dalí and legendary animator Walt Disney began collaborating on a short film that was not completed until 2003, years after both men had died.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

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.

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.

During the French Revolution, a botanist's letter asking about "dear Rhus" (poison ivy) was intercepted, leading authorities to suspect he was conspiring with the Russians.

The Brothers Grimm were lawyers before they were storytellers, and became interested in fairy tales as they began investigating how rules and customs had been passed down through cultures.

The story of Dollree Mapp, whose legal challenge over her 1957 conviction for possessing "obscene material" led to a major strengthening of the Fourth Amendment

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

'Shogun,' a 1980s TV series, helped popularize sushi in the US by stimulating an American interest in Japanese culture.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

Meet the 56 signers of the Declaration of Independence—most of whom didn't put pen to paper until August 2, 1776—and see their original signatures.

Domino's Pizza's 30-minute delivery guarantee was responsible for the chain's 1980s surge, but it was discontinued after the company was found liable for delivery driver accidents.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

In 2026, Finland was named the world's happiest country for the ninth consecutive year based on its wealth, social safety network, and high life expectancy, among other factors.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'