September 1–27, 1939 · Eastern Europe Theater

Germany invaded Poland from the west on September 1st with 1.5 million troops, using Blitzkrieg — coordinated tanks, motorized infantry, and dive bombers — to shatter Polish defenses. On September 17th, the Soviet Union invaded from the east under the secret Molotov-Ribbentrop Pact. Warsaw surrendered September 27th. Poland was divided between Nazi Germany and the Soviet Union.

May 10 – June 25, 1940 · Western Europe Theater

Germany bypassed France's Maginot Line by driving armored columns through the 'impassable' Ardennes Forest, cutting Allied forces in two. 338,000 Allied troops were evacuated from Dunkirk in a desperate naval operation using everything from destroyers to fishing boats. France signed an armistice on June 22nd; Paris fell without a fight. In six weeks Germany had done what it couldn't do in four years of WWI.

June 10, 1940 – May 13, 1943 · North Africa Theater

A see-saw campaign across the North African desert lasting nearly three years. Rommel's Afrika Korps nearly captured the Suez Canal before being halted at El Alamein. Montgomery's victory at El Alamein in November 1942 was the first major British land victory of the war. American forces landed in Operation Torch; the Axis forces were squeezed from both sides and surrendered in Tunisia in May 1943.

July 10 – October 31, 1940 · Western Europe Theater

The first major campaign fought entirely by air forces. The Luftwaffe attempted to destroy the RAF as a prelude to Operation Sea Lion — the invasion of Britain. RAF Fighter Command, using radar and the Spitfire and Hurricane, inflicted unsustainable losses. When Hitler shifted attacks to bombing London (the Blitz), it gave RAF airfields time to recover. Germany never achieved air superiority.

June 22 – December 5, 1941 · Eastern Front Theater

The largest military operation in history — 3.8 million Axis troops invaded the Soviet Union on a 1,800-mile front. Three army groups drove toward Leningrad, Moscow, and Kiev. Soviet forces collapsed in catastrophic encirclements; 3.5 million Soviet soldiers were captured in the first five months. But the vast distances, early winter, and fierce Soviet resistance slowed the advance. German forces were stopped short of Moscow in December.

December 7, 1941 · Pacific Theater

Japan's surprise carrier-based air attack on the US Pacific Fleet at Pearl Harbor, Hawaii brought America into the war. 353 Japanese aircraft in two waves sank or damaged 19 ships (including 8 battleships), destroyed 188 aircraft, and killed 2,403 Americans. The three American aircraft carriers were at sea and survived.

June 4–7, 1942 · Pacific Theater

The decisive naval battle of the Pacific war. American codebreakers had broken Japanese naval codes and knew the attack was coming. In a few critical minutes on June 4th, American dive bombers found the Japanese carriers refueling aircraft — decks covered in fuel hoses and ordnance — and sank four fleet carriers. Japan lost Akagi, Kaga, Soryu, and Hiryu, along with hundreds of irreplaceable experienced aviators.

August 23, 1942 – February 2, 1943 · Eastern Front Theater

The most destructive battle in human history. Germany's 6th Army fought its way into Stalingrad in brutal street-by-street, building-by-building combat. Soviet General Zhukov then launched Operation Uranus, encircling the entire 6th Army. Hitler refused to allow a breakout. Paulus's 300,000 men slowly starved and froze through the Russian winter. On February 2nd, 1943, 91,000 survivors surrendered.

July 4–23, 1943 · Eastern Front Theater

The largest tank battle in history — over 6,000 tanks on both sides. Germany's Operation Citadel aimed to eliminate the Kursk salient and regain the initiative. Soviet intelligence had obtained the German plans; Zhukov built massive defensive belts and waited. The German attack stalled in deep Soviet defenses. The Soviets then launched their own massive counteroffensives, beginning the great drive westward.

June 6, 1944 · Western Europe Theater

The largest amphibious invasion in history. 156,000 Allied troops landed on five Normandy beaches — Utah, Omaha, Gold, Juno, Sword — supported by 11,000 aircraft and 7,000 naval vessels. Omaha Beach saw the bloodiest fighting; American troops were cut down in the surf under withering German fire. By nightfall the Allies had established a beachhead. The liberation of Western Europe had begun.

September 17–25, 1944 · Western Europe Theater

Montgomery's bold plan to end the war by Christmas: drop three airborne divisions behind German lines to seize key bridges in the Netherlands, then rush armored columns up a single highway to cross the Rhine at Arnhem. The first two bridges were taken; at Arnhem, the British 1st Airborne Division landed near two SS Panzer divisions resting after Normandy. 'A bridge too far' — the division was destroyed; the Rhine crossing failed.

December 16, 1944 – January 25, 1945 · Western Europe Theater

Germany's last major offensive in the West. Through fog and overcast that grounded Allied air power, three German armies attacked through the Ardennes, creating a 'bulge' in Allied lines and nearly splitting them. American forces were encircled at Bastogne; General McAuliffe's reply to German demands for surrender was a single word: 'NUTS!' When the weather cleared, Allied air power destroyed the German spearheads.

February 19 – March 26, 1945 · Pacific Theater

US Marines landed on a volcanic island defended by 22,000 Japanese troops in an elaborate network of tunnels, bunkers, and caves. General Kuribayashi's strategy was to inflict maximum casualties rather than defend the beaches. The Marines fought yard by yard through the underground defenses. The iconic flag-raising on Mount Suribachi was captured in the war's most famous photograph. Of the 22,000 Japanese defenders, only 216 survived.

April 16 – May 2, 1945 · Eastern Front Theater

The final battle of the European war. 2.5 million Soviet troops with 6,000 tanks converged on Berlin. Hitler refused to leave his underground bunker as the city burned around him. On April 30th he committed suicide. Soviet soldiers raised the Red Flag over the Reichstag. On May 2nd the Berlin garrison surrendered; V-E Day followed on May 8th.

August 6 & 9, 1945 · Pacific Theater

The B-29 Enola Gay dropped 'Little Boy' on Hiroshima on August 6th, instantly killing 70,000–80,000 people; tens of thousands more died later from radiation. 'Fat Man' fell on Nagasaki three days later, killing 40,000 immediately. Japan announced surrender on August 15th. The formal surrender ceremony was held September 2nd on the deck of USS Missouri in Tokyo Bay.