World War II Summary

  • Last updated on November 11, 2022

World War II was the largest, most destructive, and most widespread war in history. During the conflict, more than 50 million people died and hundreds of millions were wounded, physically and psychologically. The war, fought on land, sea, and air, was the epic struggle of the twentieth century and was central to the whole century. It was caused in large part by the unresolved issues of World War I (1914–1918), and its aftermath became the Cold War (1945–1991).

World War II was the largest, most destructive, and most widespread war in history. During the conflict, more than 50 million people died and hundreds of millions were wounded, physically and psychologically. The war, fought on land, sea, and air, was the epic struggle of the twentieth century and was central to the whole century. It was caused in large part by the unresolved issues of World War I (1914–1918), and its aftermath became the Cold War (1945–1991).

Two coalitions of nations, the Axis and the Allies, fought the war. The Axis states were fascist and militaristic. Fascism was an extreme form of racist nationalism under the leadership of dictators who claimed to express the collective will of their peoples. The major powers of the Axis were Germany, Italy, and Japan. The major Allied Powers were Great Britain, France, the United States, and the Soviet Union. Some nations switched allegiances during the war. Italy changed sides in 1943. After 1940, France had forces on both sides, the Free French and Vichy French. The Soviet Union cooperated with Germany until attacked in June, 1941, and the United States did not officially participate until attacked by Japan on December 7, 1941.

T<sc>ime</sc> L<sc>ine of</sc> W<sc>orld</sc> W<sc>ar</sc> IIDec., 1937-Jan., 1938Japanese troops invade China, beginning World War II in East Asia.Sept. 15–29, 1938British and German leaders meet in Munich.Aug., 1939The possibility of American involvement in the war developing in Europe and East Asia prompts conversion of domestic production to meet military needs.Sept. 1, 1939Germany invades Poland, beginning World War II in Europe.Sept. 3, 1939-May 4, 1945Battle of North Atlantic: Eventual definitive victory for Allied forces.Oct., 1939-Dec. 7, 1941Polish Campaign.Apr. 9, 1940Germany invades Norway.May-June, 1940Germany occupies France.May 10, 1940Germany invades Luxembourg, the Netherlands, and Belgium.June 10, 1940Italy declares war on France and Great Britain. Italian forces enter southern France.July 10-Oct. 31, 1940Battle of Britain: Germany bombs Great Britain in preparation for a land invasion. Despite great losses on both sides, the British repulse German air power and avoid German occupation.Sept. 27, 1940Japan signs the Tripartite Pact with Germany and Italy, becoming a member of the Axis powers.Oct. 8, 1940Germany begins occupation of Romania.Oct. 28, 1940Italy invades Greece.Nov. 11, 1940Battle of Taranto.Dec. 9–13, 1940Battle of Sīdī Barrāni.1941–1942Battle of Moscow.1941–1944Siege of Leningrad.Mar. 11, 1941Before the United States becomes formally involved in the war, it uses the Lend-Lease program to support Great Britain’s war effort while declaring official neutrality.May 20–31, 1941Crete campaign.July 24, 1941Japan occupies French Indochina (modern Vietnam). United States halts trade with Japan, sends General Douglas MacArthur to oversee military forces in the Philippines.Sept. 16–26, 1941Battle of Kiev.Nov. 18, 1941-June 21, 1942Battles of Tobruk.Dec., 1941-Apr., 1942Battle of Bataan: A Japanese victory that is a major step in Japan’s attainment of the Philippines.Dec. 7, 1941Battle of Pearl Harbor: Japanese bomb Pearl Harbor in the Hawaiian Islands, sinking or disabling five of eight U.S. battleships, as well as other ships and airplanes. Nearly 2,500 persons, including 68 civilians are killed. Japan simultaneously attacks Guam, the Philippines, Midway Island, Hong Kong, and the Malay Peninsula.Dec. 8, 1941United States declares war on Japan.Dec. 10, 1941-Feb. 15, 1942Battle of Singapore.Dec. 11, 1941Axis nations declare war on the United States.1942–1943Battles of Kharkov.Feb. 19, 1942U.S. government begins relocating persons of Japanese descent on the Pacific Coast.Feb. 27-Mar. 1, 1942Battle of the Java Sea: Severe U.S. losses; Japan occupies Java.Mar. 9, 1942Japan occupies Rangoon, Burma, cutting off Allied access to China.May 3–8, 1942Battle of the Coral Sea: For the first time in history, all fighting in a naval battle is conducted by planes launched off aircraft carriers. Japanese advance into Australia is halted.May 6, 1942Bataan Peninsula and Corregidor fall to the Japanese.June 3–21, 1942Japan bombs Alaska, occupies the Aleutian Islands, and shells the Oregon coast.June 3–5, 1942Battle of Midway: Japan’s advance across the Pacific is stopped, and Japan suffers severe losses. Turning point in the Pacific war.June 17, 1942President Roosevelt approves the Manhattan Project, which is to build an atomic bomb.Aug. 7, 1942-Feb. 9, 1943Battle of Guadalcanal: United States prevents Japanese from landing reinforcements, ensuring Allied conquest of Guadalcanal. Japanese evacuate Guadalcanal on Feb. 9, 1943.Aug. 19, 1942Raid on Dieppe.Aug. 23, 1942-Feb. 2, 1943Battle of Stalingrad.Aug. 23–25, 1942Battle of Eastern Solomons: United States inflicts severe damage on Japanese ships.Sept. 13–14, 1942Battle of Bloody Ridge: Six thousand Japanese troops are routed.Oct. 23-Nov. 4, 1942Battle of El Alamein.Nov. 7–8, 1942North Africa Invasion: An Allied campaign designed to drive the Germans out of North Africa, this operation provides a training ground for U.S. forces in World War II.Feb., 1943Casablanca Conference.July 5–15, 1943Battle of Kursk.July 6, 1943Battle of Kula Gulf: First U.S. victory in South Pacific.July 9-Sept. 19, 1943Italy Invasion: This campaign forces Germany to use troops and resources that might otherwise have been used in northern France.Aug. 15, 1943United States regains Aleutian Islands.Sept. 8, 1943Italy surrenders unconditionally.Sept. 9-Oct. 1, 1943Battle of Salerno: The Allies accomplish their objective, taking the port of Naples.Nov., 1943-June, 1944Battle of Monte Cassino.Nov. 2, 1943Battle of Empress Augusta Bay: Japanese defeat in South Pacific secures Solomons for the Allies.Nov. 20–23, 1943Battle of Tarawa: Costly U.S. victory in which U.S. forces use the captured airstrip to support invasions of the Marshall Islands.Jan. 22-May 25, 1944Battle of Anzio.Jan. 31-Nov. 25, 1944United States takes Marshall Islands, Mariana Islands, Guam, and the Palaus.June 6, 1944D Day: Operation Overlord’s Normandy invasion begins.June 15-July 9, 1944United States seizes the island of Saipan, headquarters for the Japanese defense of the Central Pacific. Its fall impairs the Japanese defense strategy and gives the Americans an air base from which B-29 Superfortress bombers can reach Tokyo.June 15, 1944Superfortress bombing of Japan begins.June 19–20, 1944Battle of the Philippine Sea: Inflicts severe losses on Japan, of both sea vessels and airplanes.June 22-July 11, 1944Soviets send 166 divisions against German positions in Belorussia in Operation Bagration.July20-Aug. 10,1944Battle of Guam: United States recaptures a strategic base in the Pacific from the Japanese.July 24-Aug. 1, 1944Battle of Tinian: United States swiftly takes Tinian from the Japanese; it becomes the launching site for numerous B-29 bombing raids against the Japanese main islands.Aug. 25, 1944Liberation of Paris.Sept. 11, 1944Liberation of Luxembourg.Sept. 17–26, 1944Battle of Arnhem.Oct. 23–26, 1944Battle of Leyte Gulf: In three major naval engagements, United States destroys remaining Japanese naval forces and takes control of Philippines. The largest naval battle of the war.Dec. 16, 1944-Jan. 25, 1945Battle of the Bulge: German forces are routed in a desperate campaign to halt advancing Allied armies.Feb. 4–11, 1945Yalta Conference: This significant meeting of the “Big Three” Allied powers marks the height of Allied cooperation but also reveals conflicting agendas.Feb. 19-Mar. 26, 1945Battle of Iwo Jima: U.S. Marines seize a Japanese island air base located southeast of Japan.Mar., 1945Battle of Mandalay.Mar. 7-May 8, 1945Rhine Crossings.Apr. 1-July 2, 1945Battle of Okinawa: United States invades Okinawa, occupying it by June 21. Japanese suicide flights contribute to making this the costliest battle of the war.Apr. 19-May 2, 1945Battle of Berlin.May 7, 1945Germany signs surrender documents.May 8, 1945V-E Day: President Harry S. Truman declares victory in Europe.July 17-Aug. 2, 1945Potsdam Conference: The third and final “Big Three” meeting plans a peace settlement at the end of World War II.Aug. 6 and 9, 1945United States drops atomic bombs on Hiroshima and Nagasaki, Japan.Aug. 14, 1945V-J Day: Japan accepts terms of surrender and occasion is declared “Victory in Japan” day.
Causes of the War

World War II grew out of grievances produced by the aftermath of World War I. Germans were outraged by the harsh Treaty of Versailles (1919), which had taken away German territory in the east and west, destroyed the Austro-Hungarian Empire, humiliated Germans by including a “war guilt” clause, imposed disarmament, and demanded payments for war damage. Racked by inflation and depression, a substantial minority of Germans voted the extremist Nazi Party into power in 1933. Adolf Hitler, the charismatic and fanatical nationalist, pursued policies of economic control and rearmament. The Nazis were both anticommunist and anti-Semitic, blaming Reds and Jews for Germany’s problems. Hitler saw a need for “living space” for “superior” Germans, which was to be carved from lands occupied by “inferior” Slavic peoples living to the east.

Hitler pursued a policy of aggression in foreign policy, with the express aim of bringing all ethnic Germans into the new Reich, or empire. German forces entered the demilitarized German Rhineland in 1936, Austria in 1938, and Czechoslovakia in 1938 and 1939. Meanwhile, Britain and France sought to appease the Nazis by granting concessions in the hope that this would satisfy German ambitions. The height of the policy of appeasement came at the Munich Conference in 1938, which dismembered Czechoslovakia. However, in the eyes of the Western democracies, concessions to Hitler appeared only to encourage more aggression. Britain and France decided to guarantee the integrity of several small states in Europe, including Poland.

Hitler’s demands on Poland centered on the surrender of territory that had been shifted from Germany to Poland after World War I, particularly the Polish corridor and the city of Danzig. The Poles resolved to resist dismemberment of their country, and World War II began on September 1, 1939, when Germany attacked Poland. Britain and France honored their commitment to Poland and went to war.

Just before attacking Poland, Hitler made an unexpected agreement, the German-Soviet Pact of 1939, with Soviet leader Joseph Stalin. It called for peace and economic cooperation between Germany and the Soviet Union and divided Poland between them. It was Stalin’s hope that Germany and the Western powers would destroy themselves while a neutral Soviet Union would continue to gain strength.

Italy did not join the war on the German side until 1940. Italy had been appeased when it attacked Ethiopia in 1935. Another important fascist state, Spain, whose leader, Francisco Franco, had been aided by the Germans during its civil war of 1936, managed to remain neutral throughout the war.

A major question decided by World War II was whether Germany or the Soviet Union would dominate the lands of Eastern Europe and control the Poles, Czechs, Slovaks, Hungarians, and many South Slavs. Germans had enjoyed economic predominance in this area for centuries, and Russians had long regarded the Slavic peoples as ethnic and cultural relatives who needed their protection. The Russo-German phase of the war, beginning with the sudden German invasion of the Soviet Union in June, 1941, brought the war’s most ferocious fighting and worst attrition to the plains of Eastern Europe. Before the invasion of the Soviet Union, some military leaders had favored a war against the Soviet Union.

German chancellor Adolf Hitler receiving an ovation from the Reichstag after announcing his annexation of Austria in March, 1938. (National Archives)

Soviet foreign minister Vyacheslav Molotov signs the German-Soviet nonaggression pact in Moscow on August 23, 1939, while Soviet premier Joseph Stalin (in white jacket) and German foreign minister Joachim von Ribbentrop (behind Molotov) look on. (National Archives)

The War in Asia

The war in Asia began earlier, in 1931, when Japan moved against the rich Chinese province of Manchuria. Japan had modernized rapidly and wanted the province’s raw materials for its industries. Military figures came to dominate Japanese domestic politics as ruthless aggression led to a full-scale war between Japan and China. The United States favored China and began an anti-Japanese foreign policy that ultimately led to the Japanese attack on Pearl Harbor. Both Japan and the United States had large naval forces in the Pacific. One of the great questions to be decided by World War II was which of these nations would dominate the Pacific.

Japan signed a defensive pact with Germany and Italy in 1936. Partly as a result of Germany’s success in invading the Soviet Union in 1941, the Japanese decided to strike southward against the European nations’ holdings in Asia. By attacking European holdings in Asia, Japan could claim to be freeing Asians from European rule. Southeast Asia would give Japan an abundance of resources, particularly oil and rubber. Japan and the Soviet Union maintained neutrality toward each other until the Soviets attacked the Japanese in 1945.

Only the U.S. Navy stood in the way of Japan. The United States had a large, modern navy, divided between the Atlantic and the Pacific. President Franklin D. Roosevelt sought to curtail Japanese expansion in Asia at the same time that he opposed German advances in Europe. He had the utmost concern for the plight of Britain in 1940, when Britain stood alone in Europe against Hitler. Like many Americans, Roosevelt thought that German victory in Europe would bring tyranny to millions and eventually threaten democracy in the United States as well. What hampered Roosevelt from joining outright in Britain’s defense was very strong isolationist sentiment in the United States. Isolationists did not want to support or participate in foreign wars, which they claimed had nothing to do with the United States. Roosevelt could not risk deeply offending the isolationists because he needed their support to be reelected. However, he gave as much aid to Britain as possible under legislative constraints, allowing the U.S. Navy to help protect convoys destined for Britain.

Pacific Theater of World War II

When Japan launched a surprise attack on Pearl Harbor on December 7, 1941, World War II took on its full global dimensions. Shortly afterward, Germany declared war on the United States. As 1942 began, all the major powers were engaged in the conflict. Land, sea, and air forces contended throughout the globe.

The War in Europe

Germany’s September 1, 1939 attack on Poland utilized new techniques of air assault and armored breakthrough, called Blitzkrieg, or lightning war. Planes would bomb to disrupt ground operations while tanks, mobile guns, and mechanized infantry would punch through a soft spot and race to surround defending forces. The Germans defeated poorly equipped Polish forces by September 28. The British and French did not attack Germany’s lightly defended western border but stayed on the defensive. Meanwhile, a desultory war at sea began, featuring submarine sinkings and sorties by units of the German surface fleet. The calm in the west in the fall and winter of 1939–1940 was called the “Phony War.”

The storm broke in the west in April of 1940 when Hitler launched a swift campaign against Denmark and Norway. Naval units, parachute troops, and transport planes boldly carried out the Norwegian invasion. British forces landed in northern Norway but could not prevail without air cover.

The Netherlands fell next as German troops swarmed across the border and planes dropped bombs on the region. Hitler adopted a daring strategy for his western offensive. While the Allies sent their forces north to defend Belgium, just as they had during World War I, German armored units lined up to storm through the rough terrain of the almost undefended Ardennes forest, the least likely access route to France. German tanks broke out and crossed below the Allied armies and raced to the sea.

The Allies had more troops and more tanks than the Germans, but the superior tactics and communication and air power of the Germans soon caused the French and British armies to retreat in panic. Hundreds of thousands of Allied troops were surrounded at Dunkirk, a northern French port. Instead of crushing them with armor, Hitler elected to allow the Luftwaffe (German air force) to destroy these forces from the air. They failed, in part because of the resistance of the Royal Air Force (RAF) and also because a great flotilla of varied ships arrived from Britain to evacuate soldiers. Through these actions, Britain’s defeat became a heroic retreat. In May, 1940, the Germans renewed the attack on France, which surrendered in June. Northern France was occupied, and Vichy France, a collaborating fascist state, was established under General Henri-Philippe Pétain in southern France. General Charles de Gaulle escaped to Britain, where he came to lead the Free French forces worldwide.

World War II saw the introduction of paratroops to combat, making it possible for the first time for combatants to place large numbers of troops behind enemy lines quickly. (National Archives)

As France collapsed, the British government changed hands. Prime Minister Neville Chamberlain was replaced by Winston S. Churchill, who had always opposed appeasing the Germans. Britain stood all alone, except for its overseas empire, and faced a continent dominated by Hitler. In stirring and famous speeches, Churchill vowed to fight to the death. Hitler was not as eager to fight the British as he was to fight the Soviets, who were still helping him, because he saw the British as racially similar to the Germans. Nevertheless, he tried to subdue Britain in the summer of 1940. Before he could mount an invasion, he had to establish German superiority in the air. The Battle of Britain was fought entirely in the air from July to November, 1940. The Luftwaffe could not destroy the RAF and suffered substantial losses in the effort.

Thwarted, Hitler turned his attention to preparing for a land campaign against the Soviet Union. However, German forces continued mass night bombings of British cities, a tactic known as the Blitz. London was particularly hard hit, but Londoners showed amazing bravery and determination. Britain was also threatened on the seas by a growing submarine campaign against merchant ships, which provided the imports necessary to sustain industry and feed the nation. The Battle of the North Atlantic, which raged all through the war, destroying many British ships, greatly worried Churchill.

European Theater of World War II

Italy joined the war as France collapsed, hoping to gain more territory in Africa. Italy launched unsuccessful campaigns against British forces in North Africa in the summer of 1940 and against Greece in October, 1940. German forces had to rescue Italian troops in both campaigns. To save the Italians, Hitler had to conquer the Balkans and send the German Afrika Corps to North Africa, led by General Erwin Rommel.

North Africa was only a sideshow for the Axis, however. The great campaign of 1941 was Operation Barbarossa, in which more than three million German and Axis forces attacked the Soviet Union. Victory followed victory as German forces advanced on a three-pronged front, aiming at Leningrad, Moscow, and Ukraine. Many people thought that the Soviet collapse was near, but despite fearful losses, the Russians held on until mud and cold stalled the German invasion. The Germans had expected victory before winter and were unprepared for Russia’s bitter cold.

The United States Enters the War

When Japan attacked Pearl Harbor (December 7, 1941), the Germans were about to be thrown back on the outskirts of Moscow. The brilliant surprise attack sank U.S. battleships but U.S. carriers were at sea. Japanese strategy called for the rapid conquest of Southeast Asia after crippling the U.S. fleet. U.S. forces held out in the Philippines as long as possible, but Japanese forces stormed to victory all through the area, easily conquering the British bastion of Singapore (1941–1942). Nevertheless, American leaders decided that Japan was less of a threat than Nazi Germany and gave the war in Europe first priority for the rapidly expanding U.S. forces.

At the beginning of 1942, the Axis Powers were at the height of their expansion, dominating continental Europe and the western Pacific. The Soviet Union appeared about to collapse, and Britain was being strangled by submarine warfare. The United States was unable to stop the victorious Japanese fleet. Then the course of the war changed through three dramatic turning points: the Battles of Coral Sea (May 3–8, 1942), Midway (June 4, 1942), and Guadalcanal (August 7, 1942-February 9, 1943), when the tide turned against the Japanese in the Pacific; El Alamein (October 23-November 4, 1942) in North Africa, where Rommel was defeated by Bernard Law Montgomery at the outskirts of Egypt; and the most important battle of all, Stalingrad (August 23, 1942-February 2, 1943) along the Volga River, deep in the Soviet Union, which threw the Germans back.

The Russian Front

The hitherto invincible German army was destroyed on the plains of Russia. Four out of five German casualties in the war occurred on this battle site, at the cost of more than twenty million Soviet lives. In 1942, Hitler planned to drive his troops to the southeast to capture oil fields in the Caucasus. When his forces became bogged down in Stalingrad, the campaign foundered. The Soviets launched a counterattack that surrounded the city and eventually forced a stunning German surrender. An even more destructive defeat occurred at Kursk (July, 1943) in the Ukraine. Until 1943, the Germans had advanced in the summer and the Soviets had pushed them back in the winter. Beginning in 1943, however, Soviet forces advanced westward in the summer and winter, arriving in eastern Europe by 1944 and in Berlin in 1945. The fighting on the eastern front was vicious and included the mass murder of civilians and prisoners by both sides.

Stalin constantly called for a “second front,” meaning an Allied invasion in Western Europe. Anglo-American forces were cautious, first invading North Africa in November, 1942, and Italy in 1943. The Italians changed sides and eventually executed Italian leader Benito Mussolini. Meanwhile, the great Allied bombing offensive against German cities intensified, which drew German forces from the critical eastern front. Simultaneously, the convoy system, long-range air power, and new equipment diminished the submarine menace.

U.S. wartime production became phenomenal. Massive numbers of ships, planes, tanks, and guns poured out of factories to equip U.S. and Allied forces. Powerful trucks, landing craft, and rapidly evolving aircraft were particularly important American contributions to the war. Women took jobs hitherto reserved for men in all countries involved in the war.

A more sinister operation gained speed in German-occupied Europe: the deliberate mass killing of Jews and other groups, a well-documented event called the Holocaust. More than eight million Jews and three million others were murdered in concentration camps.

Allied Victory

The long-expected Allied invasion of Europe took place June 6, 1944, at Normandy, long after the Soviets had begun to push back the German armies on the eastern front. Breakout and the liberation of Paris followed, due in large measure to the actions of General George S. Patton. General Montgomery’s plan to cross the Rhine via Holland, Operation Market Garden, September, 1944, failed. A surprise German attack in Belgium in December, 1944, the Battle of the Bulge, temporarily caused the Allies concern. Yet by the spring of 1945, they were able to push deep into Germany and link up with Soviet forces, which reached Berlin in April, 1945. The war in Europe came to an end after Hitler committed suicide in a Berlin bunker as Soviet troops conquered the city.

Meanwhile, U.S. forces under Douglas MacArthur in the Pacific liberated the Philippines (October, 1944-July, 1945), and Chester W. Nimitz used the dramatically expanded U.S. Navy in an island-hopping campaign. The Japanese fleet and air forces were virtually wiped out in a series of one-sided battles. When islands close to Japan–Iwo Jima (February-March, 1945) and Okinawa (April-July, 1945)–were seized, the Japanese turned to suicidal kamikaze attacks against U.S. ships. An invasion of Japan was planned, but became unnecessary after the world’s first atomic bombs were dropped on Hiroshima and Nagasaki in August, 1945. Japan surrendered but was allowed to keep its emperor.

Many of the inmates of Germany’s Buchenwald concentration camp were barely alive when Allied troops liberated the camp in April, 1945. (National Archives)


The results of World War II largely determined the course of the rest of the century. Devastated Germany was shorn of territory to the east, west, and south, and was partitioned and occupied. The Soviet Union replaced Germany as the dominant power in Eastern Europe as communist puppet states emerged in the shadow of the Red Army. Bombed-out Japan was occupied by the now clearly dominant power in the Pacific, the United States.

The postwar world was soon overshadowed by the Cold War, as the Soviet sphere in Europe was delineated by what Churchill came to call the Iron Curtain. Western Europe was uplifted and protected by the United States. The generous Marshall Plan poured millions of dollars into non-communist countries to bolster their resistance to communism and eventually to make them good business partners for the United States. Observers expected Western Europe to take generations to recuperate, but Europe recovered with surprising rapidity.

As Supreme Allied Commander in the Pacific, General Douglas MacArthur signs the formal documents recognizing Japan’s surrender in the war. The ceremony took place aboard the battleship USS Missouri, anchored in Tokyo Bay, on September 2, 1945. (National Archives)

The ideology of fascist racism was thoroughly discredited by the war. Communism in the Soviet bloc continued until the Soviet Union’s dissolution during the early 1990’s. The Cold War’s key confrontation was the border between democratic West Germany and communist East Germany.

The United States emerged from the war as a global superpower with its productive capacities hugely expanded by the war. National pride and confidence in democracy and capitalism flourished as wealth and power soared. Overall, Americans and their allies looked back on the war, terrible as it was, as a necessary struggle to preserve freedom.

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