World War II

The Second Sino-Japanese War Begins

A clash between Japanese and Chinese troops at the Marco Polo Bridge (Lugou Bridge) near Beijing escalated within weeks into a full-scale Japanese invasion of China. Following the Battle of Shanghai, Japanese forces captured the Nationalist capital of Nanjing later that year.

Why it matters: The fighting that began at the Marco Polo Bridge is widely treated as the opening of World War II in Asia and the Pacific — years before war broke out in Europe.

The Munich Agreement

Germany, Italy, Britain, and France signed the Munich Agreement, forcing Czechoslovakia — which was not party to the talks — to cede its German-speaking Sudetenland border region to Nazi Germany. British Prime Minister Neville Chamberlain and French Premier Édouard Daladier accepted Hitler's demands in the belief they had preserved peace.

Why it matters: Munich became the defining symbol of 'appeasement.' Hitler seized the rest of Czechoslovakia in March 1939, and within a year Europe was at war.

The Nazi-Soviet Pact

German Foreign Minister Joachim von Ribbentrop and Soviet Foreign Minister Vyacheslav Molotov signed a ten-year nonaggression pact. A secret protocol divided eastern Europe into German and Soviet spheres of influence and agreed to partition Poland.

Why it matters: The pact freed Hitler to attack Poland without fear of a two-front war. Less than two years later Germany invaded the Soviet Union, breaking it.

How we know: The public treaty and its secret protocol dividing Poland are documented in the historical record.

Germany Invades Poland

Germany launched an unprovoked invasion of Poland at dawn, spearheaded by tanks and aircraft. Britain and France declared war on Germany on September 3. Warsaw fell at the end of September, and the Soviet Union invaded from the east on September 17.

Why it matters: The invasion of Poland began World War II in Europe and triggered the British and French declarations of war.

The Fall of France and the Dunkirk Evacuation

On May 10, 1940, Germany's blitzkrieg swept through the Low Countries and into France, bypassing the Maginot Line. As Allied armies collapsed, Operation Dynamo evacuated more than 338,000 British and French troops from the beaches of Dunkirk between May 26 and June 4. Germany entered Paris on June 14, and France signed an armistice on June 22.

Why it matters: The fall of France left Britain to fight on alone in western Europe; the Dunkirk evacuation saved an army and became a symbol of defiance.

The Battle of Britain

Germany's Luftwaffe fought to win air superiority over southern England in preparation for an invasion. RAF Fighter Command, flying Hurricanes and Spitfires and aided by a pioneering radar-based air-defense network, denied the Germans control of the skies. Hitler ultimately postponed the invasion.

Why it matters: It was the first major campaign fought entirely in the air, and Britain's victory ended the immediate threat of a German invasion of the British Isles.

Operation Barbarossa: Germany Invades the Soviet Union

Germany launched Operation Barbarossa, invading the Soviet Union with roughly three million Axis troops along a vast front — the largest military operation in history. The attack broke the 1939 Nazi-Soviet Pact and opened the Eastern Front.

Why it matters: The Eastern Front became the deadliest theater of the war and the setting for much of the Holocaust; the invasion ultimately overextended and doomed Nazi Germany.

The Attack on Pearl Harbor

In a surprise attack, 353 aircraft from six Japanese carriers struck the U.S. Pacific Fleet at Pearl Harbor, Hawaii, in two waves. They sank or damaged numerous battleships and destroyed many aircraft; more than 2,400 Americans were killed. The U.S. aircraft carriers were at sea and escaped.

Why it matters: The attack brought the United States into World War II. The day after, President Roosevelt called it 'a date which will live in infamy.'

The Wannsee Conference and the 'Final Solution'

Fifteen senior Nazi and German government officials met at a villa on Berlin's Lake Wannsee to coordinate the 'Final Solution to the Jewish Question' — the systematic murder of Europe's Jews. Reinhard Heydrich outlined a plan encompassing some 11 million Jews across Europe and assigned the SS to lead the killing.

Why it matters: Wannsee did not begin the genocide, but it coordinated the machinery of the Holocaust, in which roughly six million Jews were murdered.

How we know: A surviving copy of the meeting's minutes — the Wannsee Protocol — records the participants and the plan.

The Battle of Midway

Forewarned by code-breaking, U.S. carrier forces ambushed a Japanese fleet advancing on Midway Atoll. American dive-bombers sank all four of Japan's fleet carriers in the engagement, at the cost of the carrier USS Yorktown.

Why it matters: Midway is widely regarded as the decisive battle of the Pacific war, halting Japanese expansion and shifting the initiative to the United States.

The Second Battle of El Alamein

In the Egyptian desert, General Bernard Montgomery's British Eighth Army launched a set-piece offensive against the Axis forces of Erwin Rommel, opening with a massive artillery barrage on the night of October 23. After nearly two weeks of grinding attrition, the Axis line broke and Rommel was driven into a long retreat westward.

Why it matters: El Alamein was the turning point of the North African campaign and the first major British land victory over the Germans, safeguarding the Suez Canal.

The Battle of Stalingrad Ends

After months of brutal urban fighting, a Soviet counteroffensive encircled the German Sixth Army in Stalingrad. Cut off and starving, Field Marshal Friedrich Paulus surrendered the trapped force; roughly 91,000 survivors were taken prisoner when resistance ended on February 2, 1943.

Why it matters: The destruction of an entire German army marked the turning point of the war on the Eastern Front, after which the Soviets steadily pushed Germany back.

The Allied Invasion of Italy and the Fall of Mussolini

The Allies landed in Sicily on July 10, 1943 (Operation Husky). Amid the collapse, Benito Mussolini was deposed and arrested on July 25. The new Italian government under Marshal Pietro Badoglio secretly negotiated an armistice, announced on September 8. German forces then occupied much of Italy and fought on there for the rest of the war.

Why it matters: Italy became the first Axis power to fall, opening a new front in southern Europe and knocking Mussolini's Fascist regime from power.

D-Day: The Normandy Landings

Operation Overlord, the largest amphibious invasion in history, put nearly 160,000 Allied troops ashore across five Normandy beaches — code-named Utah, Omaha, Gold, Juno, and Sword — supported by thousands of ships and aircraft under the command of General Dwight D. Eisenhower.

Why it matters: D-Day opened the long-awaited Western Front in France, beginning the liberation of northwestern Europe from Nazi occupation.

The Liberation of Paris

As Allied armies broke out of Normandy and the French Resistance rose within the city, General Philippe Leclerc's Free French 2nd Armored Division and U.S. troops entered Paris. The German garrison surrendered, and General Charles de Gaulle walked down the Champs-Élysées in triumph.

Why it matters: The liberation of the French capital was a powerful symbolic and strategic victory, restoring French self-government after four years of occupation.

The Battle of Leyte Gulf

Fought in the waters around the Philippines across four major engagements, Leyte Gulf was the largest naval battle of World War II. The U.S. Navy shattered the Imperial Japanese Navy's remaining offensive strength; the battle also saw the first organized kamikaze attacks.

Why it matters: The battle effectively destroyed Japan's fleet as a fighting force and secured the Allied return to the Philippines.

The Battle of the Bulge

Germany launched a surprise winter offensive through the forested Ardennes, aiming to split the Allied armies and reach the port of Antwerp. The attack created a large 'bulge' in the Allied line but was halted and then reversed; by late January 1945 the Allies had retaken all the lost ground.

Why it matters: Hitler's last major offensive in the west failed, exhausting Germany's reserves and hastening its collapse. It was the largest single battle fought by the U.S. Army in the war.

The Liberation of Auschwitz

Soviet troops entered the Auschwitz camp complex in occupied Poland and freed roughly 7,000 prisoners left behind — many starving and gravely ill — after the SS had forced tens of thousands of others on death marches westward. Auschwitz-Birkenau had been the largest of the Nazi killing centers.

Why it matters: The liberation exposed the machinery of the Holocaust to the world. January 27 is now observed as International Holocaust Remembrance Day.

The Yalta Conference

With Germany near defeat, the 'Big Three' — Franklin Roosevelt, Winston Churchill, and Joseph Stalin — met in the Crimean resort of Yalta to plan the war's end and the postwar order. They discussed the occupation of Germany, the future of eastern Europe and a new United Nations, and agreed the Soviet Union would enter the war against Japan.

Why it matters: Yalta's decisions shaped postwar Europe and the emerging division between the Western allies and the Soviet Union that would define the Cold War.

The Battle of Okinawa

U.S. Tenth Army forces landed on Okinawa on April 1, 1945, in the largest amphibious assault of the Pacific war. Nearly three months of ferocious fighting and mass kamikaze attacks killed tens of thousands of soldiers on both sides and enormous numbers of Okinawan civilians.

Why it matters: As the last major battle before a planned invasion of Japan's home islands, Okinawa's staggering cost weighed heavily on the decision to use the atomic bomb.

The Fall of Berlin and Hitler's Death

As the Red Army fought through Berlin, Adolf Hitler killed himself in his bunker on April 30, 1945, alongside Eva Braun, whom he had married the day before. Berlin's defenders surrendered to Soviet forces on May 2.

Why it matters: The death of the Nazi dictator and the fall of the German capital brought the Third Reich to its end and cleared the way for Germany's surrender.

V-E Day: Victory in Europe

Germany surrendered unconditionally. General Alfred Jodl signed the surrender at Eisenhower's headquarters in Reims on May 7; a second signing followed in Berlin. The Western Allies proclaimed May 8 as Victory in Europe Day, and crowds celebrated in cities across the world.

Why it matters: V-E Day ended nearly six years of war in Europe — though fighting still raged in the Pacific.

The United Nations Is Founded

Delegates of 50 nations, meeting at the San Francisco Conference, signed the Charter of the United Nations on June 26, 1945. The Charter entered into force on October 24, 1945, establishing a new international organization to maintain peace and security.

Why it matters: Created out of the determination to prevent another world war, the UN became the central institution of the postwar international order.

The Atomic Bombings of Hiroshima and Nagasaki

On August 6, 1945, the American B-29 Enola Gay dropped the uranium bomb 'Little Boy' on Hiroshima; three days later, on August 9, Bockscar dropped the plutonium bomb 'Fat Man' on Nagasaki. Each bomb destroyed most of its city and killed tens of thousands of people instantly, with many more dying later from injuries and radiation.

Why it matters: The only wartime use of nuclear weapons, the bombings preceded Japan's surrender within days and opened the atomic age.

Japan Surrenders: V-J Day

Following the atomic bombings and the Soviet declaration of war, Japan agreed to surrender. Japanese and Allied representatives signed the Instrument of Surrender aboard the battleship USS Missouri in Tokyo Bay on September 2, 1945, with General Douglas MacArthur presiding.

Why it matters: The formal surrender of Japan ended World War II — the deadliest conflict in human history.

How we know: The signed Instrument of Surrender and the documented ceremony aboard USS Missouri record the event.

The Nuremberg Trials Begin

The International Military Tribunal opened at Nuremberg, where the United States, Britain, the Soviet Union, and France jointly prosecuted senior Nazi leaders. Twenty-four defendants were indicted on charges including crimes against peace, war crimes, and crimes against humanity.

Why it matters: Nuremberg established the principle that individuals — including heads of state and their officials — can be held criminally accountable under international law, a foundation of modern human-rights law.