World War II
Clockwise from top left: Chinese forces in the Battle of Wanjialing, Australian 25-pounder guns during the First Battle of El Alamein, German Stuka dive bombers on the Eastern Front winter 1943–1944, US naval force in the Lingayen Gulf, Wilhelm Keitel signing the German Surrender, Soviet troops in the Battle of Stalingrad
Date 1 September 1939 (1939-09-01) – 2 September 1945 (1945-09-02) (&100000000000000060000006 years, &100000000000000010000001 day) Location Europe, Pacific, Atlantic, South-East Asia, China, Middle East, Mediterranean and Africa, briefly North America Result Allied victory Dissolution of the Third Reich Creation of the United Nations Emergence of the United States and the Soviet Union as superpowers Beginning of the Cold War. (more...)
Belligerents
Allies 22x20px Soviet Union (1941–45)[nb 1]  United States (1941–45)  British Empire China (at war 1937–45)  France[nb 2]  Poland  Canada  Australia  New Zealand  South Africa  Yugoslavia (1941–45)  Greece (1940–45)  Norway (1940–45)  Netherlands (1940–45)  Belgium (1940–45)  Czechoslovakia  Brazil (1942–45) ...and others Client and puppet states Philippines (1941–45) Mongolia (1941–45) ...and others	Axis  Germany  Japan (at war 1937–45)  Italy (1940–43)  Hungary (1940–45)  Romania (1941–44)  Bulgaria (1941–44) Co-belligerents  Finland (1941–44)  Thailand (1942–45) 22x20px Iraq (1941) Client and puppet states  Manchukuo  Italian Social Republic (1943–45)  Independent State of Croatia (1941–45)  Slovakia ...and others
Commanders and leaders
Allied leaders 22x20px Joseph Stalin Franklin D. Roosevelt Winston Churchill Chiang Kai-shek Charles de Gaulle ...and others	Axis leaders Adolf Hitler Hirohito Benito Mussolini ...and others
Casualties and losses
Military dead: Over 16,000,000 Civilian dead: Over 45,000,000 Total dead: Over 61,000,000 (1937–45) ...further details	Military dead: Over 8,000,000 Civilian dead: Over 4,000,000 Total dead: Over 12,000,000 (1937–45) ...further details

World War II, or the Second World War (often abbreviated as WWII or WW2), was a global war that was under way by 1939 and ended in 1945. It involved a vast majority of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis. It was the most widespread war in history, with more than 100 million people serving in military units. In a state of "total war", the major participants placed their entire economic, industrial, and scientific capabilities at the service of the war effort, erasing the distinction between civilian and military resources. Marked by significant events involving the mass death of civilians, including the Holocaust and the only use of nuclear weapons in warfare, it resulted in 50 million to over 70 million fatalities. These deaths make the war the deadliest conflict in human history.^[1]

Although Japan was already at war with China in 1937,^[2] the world war is generally said to have begun on 1 September 1939, with the invasion of Poland by Germany, and subsequent declarations of war on Germany by France and most of the countries of the British Empire and Commonwealth. Germany set out to establish a large empire in Europe. From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or subdued much of continental Europe; amid Nazi-Soviet agreements, the nominally neutral Soviet Union fully or partially invaded, occupied and annexed territories of its six European neighbours, including Poland. Britain and the Commonwealth remained the only major force continuing the fight against the Axis, with battles taking place in North Africa as well as the long-running Battle of the Atlantic. In June 1941, the European Axis launched an invasion of the Soviet Union, giving a start to the largest land theatre of war in history, which tied down the major part of the Axis' military forces. In December 1941, Japan, which aimed to dominate Asia and join the Axis, attacked the United States and European possessions in the Pacific Ocean, quickly conquering much of the West Pacific.

The Axis advance was stopped in 1942, after Japan lost a series of naval battles and European Axis troops were defeated in North Africa and, decisively, at Stalingrad. In 1943, with a series of German defeats in Eastern Europe, the Allied invasion of Fascist Italy, and American victories in the Pacific, the Axis lost the initiative and undertook strategic retreat on all fronts. In 1944, the Western Allies invaded France, while the Soviet Union regained all of its territorial losses and invaded Germany and its allies. The war in Europe ended with the capture of Berlin by Soviet and Polish troops and the subsequent German unconditional surrender on 8 May 1945. During 1944 and 1945 the United States defeated the Japanese Navy and captured key West Pacific islands, dropping atomic bombs on the country as the invasion of the Japanese Archipelago ("Home Islands") became imminent. The war in Asia ended on 15 August 1945 when Japan agreed to surrender.

The total victory of the Allies over the Axis in 1945 ended the conflict. World War II altered the political alignment and social structure of the world. The United Nations (UN) was established to foster international cooperation and prevent future conflicts. The great powers that were the victors of the war—the United States, Soviet Union, China, Britain, and France—became the permanent members of the UN's Security Council.^[3] The Soviet Union and the United States emerged as rival superpowers, setting the stage for the Cold War, which lasted for the next 46 years. Meanwhile, the influence of European great powers started to decline, while the decolonisation of Asia and Africa began. Most countries whose industries had been damaged moved towards economic recovery. Political integration, especially in Europe, emerged as an effort to stabilise postwar relations.

Chronology[link]

The start of the war is generally held to be 1 September 1939, beginning with the German invasion of Poland; Britain and France declared war on Germany two days later. Other dates for the beginning of war include the start of the Second Sino-Japanese War on 7 July 1937.^[4][5]

Others follow British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred simultaneously and the two wars merged in 1941. This article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935.^[6]

The exact date of the war's end is also not universally agreed upon. It has been suggested that the war ended at the armistice of 14 August 1945 (V-J Day), rather than the formal surrender of Japan (2 September 1945); in some European histories, it ended on V-E Day (8 May 1945). However, the Treaty of Peace with Japan was not signed until 1951,^[7] and that with Germany not until 1990.^[8]

Background[link]

World War I radically altered the political map, with the defeat of the Central Powers, including Austria-Hungary, Germany and the Ottoman Empire; and the 1917 Bolshevik seizure of power in Russia. Meanwhile, existing victorious Allies such as France, Belgium, Italy, Greece and Romania gained territories, while new states were created out of the collapse of Austria-Hungary and the Russian and Ottoman Empires.

In the aftermath of the war, irredentist and revanchist nationalism became important in a number of European states. Irredentism and revanchism were strong in Germany because of the significant territorial, colonial, and financial losses incurred by the Treaty of Versailles. Under the treaty, Germany lost around 13 percent of its home territory and all of its overseas colonies, while German annexation of other states was prohibited, reparations were imposed, and limits were placed on the size and capability of the country's armed forces.^[9] Meanwhile, the Russian Civil War had led to the creation of the Soviet Union.^[10]

The German Empire was dissolved in the German Revolution of 1918–1919, and a democratic government, later known as the Weimar Republic, was created. The interwar period saw strife between supporters of the new republic and hardline opponents on both the right and left. Although Italy as an Entente ally made some territorial gains, Italian nationalists were angered that the promises made by Britain and France to secure Italian entrance into the war were not fulfilled with the peace settlement. From 1922 to 1925, the Fascist movement led by Benito Mussolini seized power in Italy with a nationalist, totalitarian, and class collaborationist agenda that abolished representative democracy, repressed socialist, left wing and liberal forces, and pursued an aggressive foreign policy aimed at forcefully forging Italy as a world power—a "New Roman Empire".^[11] In Germany, the Nazi Party led by Adolf Hitler sought to establish a fascist government in Germany. With the onset of the Great Depression, domestic support for the Nazis rose and, in 1933, Hitler was appointed Chancellor of Germany. In the aftermath of the Reichstag fire, Hitler created a totalitarian single-party state led by the Nazis.^[12]

The Kuomintang (KMT) party in China launched a unification campaign against regional warlords and nominally unified China in the mid-1920s, but was soon embroiled in a civil war against its former Chinese communist allies.^[13] In 1931, an increasingly militaristic Japanese Empire, which had long sought influence in China^[14] as the first step of what its government saw as the country's right to rule Asia, used the Mukden Incident as a pretext to launch an invasion of Manchuria and establish the puppet state of Manchukuo.^[15] Too weak to resist Japan, China appealed to the League of Nations for help. Japan withdrew from the League of Nations after being condemned for its incursion into Manchuria. The two nations then fought several battles, in Shanghai, Rehe and Hebei, until the Tanggu Truce was signed in 1933. Thereafter, Chinese volunteer forces continued the resistance to Japanese aggression in Manchuria, and Chahar and Suiyuan.^[16]

Adolf Hitler, after an unsuccessful attempt to overthrow the German government in 1923, became the Chancellor of Germany in 1933. He abolished democracy, espousing a radical, racially motivated revision of the world order, and soon began a massive rearmament campaign.^[17] Meanwhile, France, to secure its alliance, allowed Italy a free hand in Ethiopia, which Italy desired as a colonial possession. The situation was aggravated in early 1935 when the Territory of the Saar Basin was legally reunited with Germany and Hitler repudiated the Treaty of Versailles, accelerated his rearmament programme and introduced conscription.^[18]

Hoping to contain Germany, the United Kingdom, France and Italy formed the Stresa Front. The Soviet Union, concerned due to Germany's goals of capturing vast areas of eastern Europe, wrote a treaty of mutual assistance with France. Before taking effect though, the Franco-Soviet pact was required to go through the bureaucracy of the League of Nations, which rendered it essentially toothless.^[19][20] However, in June 1935, the United Kingdom made an independent naval agreement with Germany, easing prior restrictions. The United States, concerned with events in Europe and Asia, passed the Neutrality Act in August.^[21] In October, Italy invaded Ethiopia, and Germany was the only major European nation to support the invasion. Italy subsequently dropped its objections to Germany's goal of absorbing Austria.^[22]

Hitler defied the Versailles and Locarno treaties by remilitarizing the Rhineland in March 1936. He received little response from other European powers.^[23] When the Spanish Civil War broke out in July, Hitler and Mussolini supported the fascist and authoritarian Nationalist forces in their civil war against the Soviet-supported Spanish Republic. Both sides used the conflict to test new weapons and methods of warfare,^[24] with the Nationalists winning the war in early 1939. In October 1936, Germany and Italy formed the Rome-Berlin Axis. A month later, Germany and Japan signed the Anti-Comintern Pact, which Italy would join in the following year. In China, after the Xi'an Incident the Kuomintang and communist forces agreed on a ceasefire in order to present a united front to oppose Japan.^[25]

Pre-war events[link]

Invasion of Ethiopia[link]

The Second Italo–Abyssinian War was a brief colonial war that began in October 1935 and ended in May 1936. The war was fought between the armed forces of the Kingdom of Italy (Regno d'Italia) and the armed forces of the Ethiopian Empire (also known as Abyssinia). The war resulted in the military occupation of Ethiopia and its annexation into the newly created colony of Italian East Africa (Africa Orientale Italiana, or AOI); in addition, it exposed the weakness of the League of Nations as a force to preserve peace. Both Italy and Ethiopia were member nations, but the League did nothing when the former clearly violated the League's own Article X.^[26]

Spanish Civil War[link]

The ruins of Guernica after the bombing.

Germany and Italy lent support to the Nationalist insurrection led by general Francisco Franco in Spain. The Soviet Union supported the existing government, the Spanish Republic, which showed leftist tendencies. Both Germany and the USSR used this proxy war as an opportunity to test improved weapons and tactics. The deliberate Bombing of Guernica by the German Condor Legion in April 1937 contributed to widespread concerns that the next major war would include extensive terror bombing attacks on civilians.^[27][28]

Japanese invasion of China[link]

A Chinese machine gun nest in the Battle of Shanghai, 1937.

In July 1937, Japan captured the former Chinese imperial capital of Beijing after instigating the Marco Polo Bridge Incident, which culminated in the Japanese campaign to invade all of China.^[29] The Soviets quickly signed a non-aggression pact with China to lend materiel support, effectively ending China's prior cooperation with Germany. Generalissimo Chiang Kai-shek deployed his best army to defend Shanghai, but after three months of fighting, Shanghai fell. The Japanese continued to push the Chinese forces back, capturing the capital Nanking in December 1937 and committed the Nanking Massacre.

In June 1938, Chinese forces stalled the Japanese advance by flooding the Yellow River; this manoeuvre bought time for the Chinese to prepare their defenses at Wuhan, but the city was taken by October.^[30] Japanese military victories did not bring about the collapse of Chinese resistance that Japan had hoped to achieve, instead the Chinese government relocated inland to Chongqing and continued the war.^[31]

Japanese invasion of the Soviet Union and Mongolia[link]

Soviet troops fought the Japanese during the Battle of Khalkhin Gol in Mongolia, 1939.

On 29 July 1938, the Japanese invaded the USSR and were checked at the Battle of Lake Khasan. Although the battle was a Soviet victory, the Japanese dismissed it as an inconclusive draw, and on 11 May 1939 decided to move the Japanese-Mongolian border up to the Khalkhin Gol River by force. After initial successes the Japanese assault on Mongolia was checked by the Red Army that inflicted the first major defeat on the Japanese Kwantung Army.^[32][33]

These clashes convinced some factions in the Japanese government that they should focus on conciliating the Soviet government to avoid interference in the war against China and instead turn their military attention southward, towards the US and European holdings in the Pacific, and also prevented the sacking of experienced Soviet military leaders such as Georgy Zhukov, who would later play a vital role in the defence of Moscow.^[34]

European occupations and agreements[link]

From left to right (front): Chamberlain, Daladier, Hitler, Mussolini, and Ciano pictured before signing the Munich Agreement.

In Europe, Germany and Italy were becoming bolder. In March 1938, Germany annexed Austria, again provoking little response from other European powers.^[35] Encouraged, Hitler began pressing German claims on the Sudetenland, an area of Czechoslovakia with a predominantly ethnic German population; and soon France and Britain conceded this territory to Germany in the Munich Agreement, which was made against the wishes of the Czechoslovak government, in exchange for a promise of no further territorial demands.^[36] Soon after that, however, Germany and Italy forced Czechoslovakia to cede additional territory to Hungary and Poland.^[37] In March 1939, Germany invaded the remainder of Czechoslovakia and subsequently split it into the German Protectorate of Bohemia and Moravia and the pro-German client state, the Slovak Republic.^[38]

Alarmed, and with Hitler making further demands on Danzig, France and Britain guaranteed their support for Polish independence; when Italy conquered Albania in April 1939, the same guarantee was extended to Romania and Greece.^[39] Shortly after the Franco-British pledge to Poland, Germany and Italy formalised their own alliance with the Pact of Steel.^[40]

In August 1939, Germany and the Soviet Union signed the Molotov–Ribbentrop Pact,^[41] a non-aggression treaty with a secret protocol. The parties gave each other rights, "in the event of a territorial and political rearrangement," to "spheres of influence" (western Poland and Lithuania for Germany, and eastern Poland, Finland, Estonia, Latvia and Bessarabia for the USSR). It also raised the question of continuing Polish independence.^[42]

Course of the war[link]

War breaks out in Europe[link]

Common parade of German Wehrmacht and Soviet Red Army on 23 September 1939 in Brest, Eastern Poland at the end of the Invasion of Poland. At centre is Major General Heinz Guderian and at right is Brigadier Semyon Krivoshein.

On 1 September 1939, Germany and Slovakia—a client state in 1939—attacked Poland.^[43] On 3 September France and Britain, followed by the countries of the Commonwealth,^[44] declared war on Germany but provided little support to Poland other than a small French attack into the Saarland.^[45] Britain and France also began a naval blockade of Germany on 3 September which aimed to damage the country's economy and war effort.^[46][47] On 17 September, after signing a cease-fire with Japan, the Soviets also invaded Poland.^[48] Poland's territory was divided between Germany and the Soviet Union, with Lithuania and Slovakia also receiving small shares. The Poles did not surrender; they established a Polish Underground State and an underground Home Army, and continued to fight with the Allies on all fronts outside Poland.^[49] About 100,000 Polish military personnel were evacuated to Romania and the Baltic countries; many of these soldiers later fought against the Germans in other theaters of the war.^[50] Poland's Enigma codebreakers were also evacuated to France.^[51] During this time, Japan launched its first attack against Changsha, a strategically important Chinese city, but was repulsed by late September.^[52]

Following the invasion of Poland and a German-Soviet treaty governing Lithuania, the Soviet Union forced the Baltic countries to allow it to station Soviet troops in their countries under pacts of "mutual assistance."^[53][54][55] Finland rejected territorial demands and was invaded by the Soviet Union in November 1939.^[56] The resulting conflict ended in March 1940 with Finnish concessions.^[57] France and the United Kingdom, treating the Soviet attack on Finland as tantamount to entering the war on the side of the Germans, responded to the Soviet invasion by supporting the USSR's expulsion from the League of Nations.^[55]

German troops by the Arc de Triomphe, Paris, after the 1940 fall of France.

In Western Europe, British troops deployed to the Continent, but in a phase nicknamed the Phoney War by the British and "Sitzkrieg" (sitting war) by the Germans, neither side launched major operations against the other until April 1940.^[58] The Soviet Union and Germany entered a trade pact in February 1940, pursuant to which the Soviets received German military and industrial equipment in exchange for supplying raw materials to Germany to help circumvent the Allied blockade.^[59]

In April 1940, Germany invaded Denmark and Norway to secure shipments of iron ore from Sweden, which the Allies were about to disrupt.^[60] Denmark immediately capitulated, and despite Allied support, Norway was conquered within two months.^[61] In May 1940 Britain invaded Iceland to preempt a possible German invasion of the island.^[62] British discontent over the Norwegian campaign led to the replacement of Prime Minister Neville Chamberlain with Winston Churchill on 10 May 1940.^[63]