World War II: A Complete Timeline of the Global Conflict

European Theater

On September 1, 1939, Germany invaded Poland, prompting Britain and France to declare war. Using 'Blitzkrieg' tactics, Germany crushed Polish resistance in weeks; the Soviet Union invaded from the east on September 17. A period of quiet on the Western Front, known as the 'Phoney War,' followed until April 1940, when Germany invaded Denmark and Norway to secure iron ore routes.

The main German offensive in the West began in May 1940, bypassing the Maginot Line by striking through the Ardennes Forest to overwhelm the Low Countries and France. Allied forces were pushed back to the coast, leading to the dramatic evacuation of over 338,000 soldiers from Dunkirk. By June 22, France had signed an armistice, and Germany occupied the country's northern half.

With Britain standing alone, the German Luftwaffe sought air superiority in the Battle of Britain (July-October 1940). The Royal Air Force successfully repelled the attacks, forcing Hitler to postpone his invasion and shift to the Blitz, a sustained bombing campaign against British cities. In 1941, Germany expanded its control by invading the Balkans before launching Operation Barbarossa—the massive and ultimately catastrophic invasion of the Soviet Union—on June 22, 1941, opening the vast Eastern Front.

Pacific Theater

As war began in Europe, Japan continued its campaign to dominate Asia. The Second Sino-Japanese War had raged since 1937; Japan occupied major cities but failed to defeat Chiang Kai-shek's Nationalists. Seeking resources to sustain its war effort, Japan occupied French Indochina in 1940, threatening British Malaya and the Dutch East Indies. In response, the United States, which supplied China, imposed economic sanctions, culminating in a crucial oil embargo in July 1941. This act forced Tokyo to either retreat or secure new oil sources by force, making war with the U.S. and its allies all but certain.

Pacific Theater

Following Japan's surprise attack on Pearl Harbor on December 7, 1941, its forces achieved a stunning series of victories, capturing the Philippines, British Malaya, Singapore, the Dutch East Indies, and Burma. The fall of the Philippines led to the brutal Bataan Death March. Despite the losses, the Doolittle Raid on Tokyo in April provided a crucial morale boost.

The tide began to turn at the May 1942 Battle of the Coral Sea. Though a tactical draw, it was a strategic Allied victory that halted Japan's sea-borne invasion of Port Moresby, New Guinea. The decisive moment came at the Battle of Midway (June 4–7). U.S. naval forces, aided by code-breaking intelligence, ambushed and sank four Japanese aircraft carriers, crippling their fleet and seizing the strategic initiative. In August, U.S. Marines landed on Guadalcanal, initiating a brutal, six-month campaign that marked the start of the Allied offensive.

European and North African Theaters

On the Eastern Front, Germany's advance reached Stalingrad on the Volga River. The ensuing battle, beginning in August, became a grinding struggle that consumed the German Sixth Army. In North Africa, General Erwin Rommel's Afrika Korps advanced into Egypt but was decisively stopped by British and Commonwealth forces under General Bernard Montgomery at the Second Battle of El Alamein in October-November. Shortly after, Operation Torch landed American and British forces in Morocco and Algeria, trapping Axis forces in Tunisia. Concurrently, the January 1942 Wannsee Conference formalized the 'Final Solution to the Jewish Question,' coordinating the systematic genocide of European Jews, now known as the Holocaust.

European Theater

Allied momentum grew throughout 1943. In February, the remnants of the German Sixth Army surrendered at Stalingrad, a catastrophic defeat from which the Wehrmacht never fully recovered on the Eastern Front. The tide also turned in the Battle of the Atlantic, as improved Allied tactics and technology overcame the German U-boat threat, securing vital supply lines. In May, the last Axis forces in North Africa surrendered. The Allies then used Tunisia as a springboard for the invasion of Sicily in July (Operation Husky), which led to the fall of Mussolini. Italy formally surrendered in September, though German forces occupied the country, leading to a long Allied campaign up the Italian peninsula.

The year 1944 was defined by the long-awaited invasion of Western Europe. On June 6, 1944—D-Day—the Allies launched Operation Overlord, the largest amphibious invasion in history, landing over 156,000 troops on the beaches of Normandy. After breaking out from the beachheads, Allied forces liberated Paris in August and swept across France and Belgium. However, a daring but flawed airborne assault, Operation Market Garden, failed to secure a bridgehead over the Rhine in September. As 1944 closed, Hitler launched a final, desperate counter-offensive in the Ardennes, beginning the Battle of the Bulge.

Pacific Theater

In the Pacific, the United States executed its 'island-hopping' strategy, bypassing fortified Japanese strongholds to seize strategically important islands and construct airfields, with brutal fighting on islands like Tarawa (November 1943). The June 1944 U.S. invasion of the Mariana Islands brought B-29 bombers within range of Japan. The Japanese Navy’s attempt to counter the invasion resulted in the Battle of the Philippine Sea. Nicknamed the 'Great Marianas Turkey Shoot,' the lopsided American victory destroyed over 600 Japanese aircraft, effectively ending Japan's carrier air power. This was followed in October by the invasion of the Philippines, prompting the Battle of Leyte Gulf. The largest naval battle in history, it was a decisive Allied victory that shattered the remaining power of the Imperial Japanese Navy.