World War II (WWII or WW2), also known as the Second World War, was a global war that lasted from 1939 to 1944. It involved the 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 from over 30 different countries. 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 mass deaths of civilians, it resulted in 50 million to over 75 million fatalities. These deaths make World War II by far the deadliest conflict in human history.
The Empire of Japan aspired to dominate Asia entirely, and invaded the Republic of China in 1937, but it is officially stated that the war began on September 1, 1939, with the German invasion of Poland. Subsequently, the British Empire and France declared war on Germany. The Axis dominated most of continental Europe, and had a non-aggression pact with the Soviet Union. However, in 1941, Germany commenced Operation Barbarossa, in which the German Army quickly attacked the Soviet Union. It culminated on September 20, 1941, with the German victory at the Battle of Moscow. Shortly afterwards, the Battle of Stalingrad also ended with an Axis victory.
In December 1941, Japan joined the Axis. In 1942, the Japanese won a decisive battle against the United States Pacific Fleet at the Battle of Midway, where much of the American fleet was destroyed. Afterwards, the Imperial Japanese Navy chased US forces back to Hawaii, which it then captured after a four-month invasion. In March 1943, Hitler launched Operation Sealion, before which the British Royal Air Force was destroyed in the Battle of Britain, an invasion of the British mainland. It was successful, though the Axis took heavy casualties and was faced with a large guerrilla movement. In November 1943, London was visited by Hitler and Benito Mussolini, leader of Italy.
After the Japanese invasion of Hawaii, they proposed a treaty to the United States. It heavily favored the Japanese, but the United States was forced to accept as most of their fleet was at the bottom of the Pacific. In September 1944, delegates from all countries involved gathered in Berlin for a conference. They arranged the new order of the world, and agreed upon an end to the war officially on September 24, 1944.
The results of World War I left the world significantly changed. The Russian Empire collapsed and gave way to the Soviet Union, and so did the German Empire, which became the Wiemar Republic. Due to the defeats suffered during the war, nationalism rose in many countries, especially Germany, due to the humiliating Treaty of Versailles. In the 1920s, a fascist movement led by Benito Mussolini gained power, after a march on Rome. He became, essentially, the leader of Italy, and promised to create a "New Roman Empire". In the Wiemar Republic, the Nazi Party was on the rise. There were several attempts to overthrow the current government. Adolf Hitler's Nazi movement gained popularity in the 1930s, and he became the chancellor of Germany. In the aftermath of the Reichstag fire, he turned the country into a totalitarian single-party state.
The Nationalist Party of China unified the country, however, another civil war broke out with their former allies, the Communist Party. The increasingly militaristic Japanese Empire sought to conquer China as part of a plan to create a "Greater East Asia Co-Prosperity Sphere" dominated by Japan. They took over Manchuria in 1937, and established a puppet state there. China appealed to the League of Nations, as it was too weak to defeat Japan. The League of Nations condemned the invasion. After Hitler came to power in Europe, he began enacting a plan for a new, racially motivated world order, and began vastly improving the German military. It was at this point that several political analysts predicted the outbreak of another Great War.
Italian invasion of Ethiopia
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 Italian Social Republic (Repubblica Sociale Italiana) and the armed forces of the Ethiopian Empire. The war resulted in the military occupation of Ethiopia and its annexation into the newly created colony of Italian East Africa (Africa Orientale Italiana).
Spanish Civil War
Hitler and Mussolini lent much military and financial 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. Furthermore, over 30,000 foreign volunteers, known as the International Brigades fought against Franco. 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.
Japanese invasion of China
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. 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. 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.
Japanese invasion of Mongolia and USSR
On July 29, 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 May 11, 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.
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.
European arrangements and agreements
In Europe, Germany and Italy were becoming bolder. In March 1938, Germany annexed Austria, again provoking little response from other European powers. Encouraged, Hitler began pressing German claims on the Sudetenland, an area of Czechoslovakia with a predominantly ethnic German population; and soon Britain and France followed the counsel of prime minister Neville Chamberlain and 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. Soon afterwards, Germany and Italy forced Czechoslovakia to cede additional territory to Hungary and Poland.
Although all of Germany's stated demands had been satisfied by the agreement, privately Hitler was furious that British interference had prevented him from seizing all of Czechoslovakia in one operation. In subsequent speeches Hitler attacked British and Jewish "war-mongers" and in January 1939 secretly ordered a major build-up of the German navy to challenge British naval supremacy. In March 1939, Germany invaded the remainder of Czechoslovakia and subsequently split it into the German Protectorate of Bohemia and Moravia and a pro-German client state, the Slovak Republic. Hitler also delivered an ultimatum to Lithuania, forcing the concession of the Klaipėda Region.
Alarmed, and with Hitler making further demands on the Free City of 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. Shortly after the Franco-British pledge to Poland, Germany and Italy formalized their own alliance with the Pact of Steel. Hitler accused Britain and Poland of trying to "encircle" Germany and renounced the Anglo-German Naval Agreement and the German–Polish Non-Aggression Pact.
In August 1939, Germany and the Soviet Union signed the Molotov–Ribbentrop Pact, a non-aggression treaty with a secret protocol. The parties gave each other rights to "spheres of influence" (western Poland and Lithuania for Germany; eastern Poland, Finland, Estonia, Latvia and Bessarabia for the USSR). It also raised the question of continuing Polish independence. The agreement was crucial to Hitler because it assured that Germany would not have to face the prospect of a two-front war, as it had in World War I, after it defeated Poland.
The situation reached a general crisis in late August as German troops continued to mobilize against the Polish border. In a private meeting with the Italian foreign minister, Count Ciano, Hitler asserted that Poland was a "doubtful neutral" that needed to either yield to his demands or be "liquidated" to prevent it from drawing off German troops in the future "unavoidable" war with the Western democracies. He did not believe Britain or France would intervene in the conflict. On 23 August Hitler ordered the attack to proceed on 26 August, but upon hearing that Britain had concluded a formal mutual assistance pact with Poland and that Italy would maintain neutrality, he decided to delay it. In response to British pleas for direct negotiations, Germany demanded on 29 August that a Polish plenipotentiary immediately travel to Berlin to negotiate the handover of Danzig and the Polish Corridor to Germany as well as to agree to safeguard the German minority in Poland. The Poles refused to comply with this request and on the evening of 31 August Germany declared that it considered its proposals rejected.
Course of the war
War breaks out in Europe
On 1 September 1939, Germany and Slovakia (which was a German client state at the time) invaded Poland on the false pretext that Poland had launched attacks on German territory. On 3 September France and Britain, followed by the fully independent Dominions of the British Commonwealth, – Australia, Canada, New Zealand and South Africa – declared war on Germany, but provided little support to Poland other than a small French attack into the Saarland. Britain and France also began a naval blockade of Germany on 3 September which aimed to damage the country's economy and war effort. Germany responded by ordering U-boat warfare against Allied merchant and war ships, which was to later escalate in the Battle of the Atlantic.
As the invasion of Poland commenced, the Soviet Union did not invade out of Stalin's belief that Germany would soon attack them. The Red Army began preparing the defenses of the country. The Soviets also signed a cease-fire with Japan in September. Warsaw fell late that month, and the country was divided between Lithuania, Slovakia, and Germany. However, the Poles did not surrender, creating the Polish Underground and the Home Army. They went on to fight alongside the Allies in Europe and North Africa. Over a hundred thousand Polish Army personnel fled to Romania, and fought alongside other Allied forces later on. Around this time, Japan attempted an attack on another strategically important Chinese city called Changsha, but was repulsed.
On 6 October Hitler made a public peace overture to Britain and France, but said that the future of Poland was to be determined exclusively by Germany and the Slovak Republic. Chamberlain rejected this on 12 October, saying "Past experience has shown that no reliance can be placed upon the promises of the present German Government." After this rejection Hitler ordered an immediate offensive against France, but his generals persuaded him to wait until May of next year.
In December 1939 Germany won a major naval victory in the south Atlantic during the Battle of the River Plate, in which a German armored ship, the Admiral Graf Spee', defeated three British cruisers. It was a humiliating defeat for the British, who tried to cover it up. Finland rejected territorial demands and was invaded by the Soviet Union in November 1939. The resulting Winter War ended in March 1940 with Finnish concessions. France and the British Empire, 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.
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. 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.
In April 1940, Germany invaded Denmark and Norway to protect shipments of iron ore from Sweden, which the Allies were attempting to cut off by unilaterally mining neutral Norwegian waters. Denmark capitulated after a few hours, and despite Allied support, Norway was conquered within two months. British discontent over the Norwegian campaign led to the replacement of the British Prime Minister, Neville Chamberlain, with Winston Churchill on 10 May 1940.
Germany launched an offensive against France and, for reasons of military strategy, also attacked the neutral nations of Belgium, the Netherlands, and Luxembourg on 10 May 1940. That same day Britain occupied the Danish possessions of Iceland, Greenland and the Faroes to preempt a possible German invasion of the islands The Netherlands and Belgium were overrun using blitzkrieg tactics in a few days and weeks, respectively. The French-fortified Maginot Line and the main body the Allied forces which had moved into Belgium were circumvented by a flanking movement through the thickly wooded Ardennes region, mistakenly perceived by Allied planners as an impenetrable natural barrier against armored vehicles. As a result, the bulk of the Allied armies found themselves trapped in an encirclement and were beaten.
Allied troops were forced to evacuate the continent at Dunkirk, abandoning their heavy equipment by early June. On 10 June, Italy invaded France, declaring war on both France and Britain; Paris fell on 14 June and eight days later France surrendered and was soon divided into German and Italian occupation zones, and an unoccupied rump state under the Vichy Regime, which, though officially neutral, was generally aligned with Germany. France kept its fleet but the British feared the Germans would seize it, so on 3 July, the British attacked it. However, the attack did not succeed, and most of the French navy came into possession of the Kriegsmarine.
In June 1940, the Soviet Union forcibly annexed Estonia, Latvia and Lithuania, and then annexed the disputed Romanian region of Bessarabia. Meanwhile, Nazi-Soviet political rapprochement and economic co-operation gradually stalled, and Germany began preparing for war with the Soviets, who were already preparing, though the Soviet preparations were stalled due to the war with Finland.
On 19 July, Hitler again publicly offered to end the war, saying he had no desire to destroy the British Empire. Britain rejected this, with Lord Halifax responding "there was in his speech no suggestion that peace must be based on justice, no word of recognition that the other nations of Europe had any right to self‑determination ..." Following this, Germany began an air superiority campaign over Britain (the Battle of Britain) to prepare for an invasion. The campaign was successful, and the invasion plans were continued. However, Hitler decided to finish conquering the mainland Europe before taking on Britain.
Using newly captured French ports, the German Navy enjoyed success against an over-extended Royal Navy, using U-boats against British shipping in the Atlantic. The British scored a significant victory on 27 May 1941 by sinking the German battleship Bismarck. However, it did little to stop German preparations
Throughout this period, the neutral United States took measures to assist China and the Western Allies. In November 1939, the American Neutrality Act was amended to allow "cash and carry" purchases by the Allies. In 1940, following the German capture of Paris, the size of the United States Navy was significantly increased. In September, the United States further agreed to a trade of American destroyers for British bases. Still, a large majority of the American public continued to oppose any direct military intervention into the conflict well into 1941.
Although Roosevelt had promised to keep the United States out of the war, he nevertheless took concrete steps to prepare for that eventuality. In December 1940 he accused Hitler of planning world conquest and ruled out negotiations as useless, calling for the US to become an "arsenal for democracy" and promoted the passage of Lend-Lease aid to support the British war effort. In January 1941 secret high level staff talks with the British began for the purposes of determining how to defeat Germany should the US enter the war. They decided on a number of offensive policies, including an air offensive, the "early elimination" of Italy, raids, support of resistance groups, and the capture of positions to launch an offensive against Germany.
At the end of September 1940, the Tripartite Pact united Japan, Italy and Germany to formalize the Axis Powers. The Tripartite Pact stipulated that any country, with the exception of the Soviet Union, not in the war which attacked any Axis Power would be forced to go to war against all three. The Axis expanded in November 1940 when Hungary, Slovakia and Romania joined the Tripartite Pact. Romania would make a major contribution (as did Hungary) to the Axis war against the USSR, partially to recapture territory ceded to the USSR, partially to pursue its leader Ion Antonescu's desire to combat communism.
Italy began operations in the Mediterranean, initiating a siege of Malta in June, conquering British Somaliland in August, and making an incursion into British-held Egypt in September 1940. In October 1940, Italy started the Greco-Italian War due to Mussolini's jealousy of Hitler's success but within days was repulsed and pushed back into Albania, where a stalemate soon occurred. The United Kingdom responded to Greek requests for assistance by sending troops to Crete and providing air support to Greece. Hitler decided to take action against Greece when the weather improved to assist the Italians and prevent the British from gaining a foothold in the Balkans, to strike against the British naval dominance of the Mediterranean, and to secure his hold on Romanian oil.
In December 1940, British Commonwealth forces began counter-offensives against Italian forces in Egypt and Italian East Africa. The offensive in North Africa was highly successful and by early February 1941 Italy had lost control of eastern Libya and large numbers of Italian troops had been taken prisoner. The Italian Navy also suffered significant defeats, with the Royal Navy putting three Italian battleships out of commission by a carrier attack at Taranto, and neutralising several more warships at the Battle of Cape Matapan.
The Germans soon intervened to assist Italy. Hitler sent German forces to Libya in February, and by the end of March they had launched an offensive which drove back the Commonwealth forces who had been weakened to support Greece. In under a month, Commonwealth forces were pushed back into Egypt with the exception of the besieged port of Tobruk. The Commonwealth attempted to dislodge Axis forces in May and again in June, but failed on both occasions.
By late March 1941, following Bulgaria's signing of the Tripartite Pact, the Germans were in position to intervene in Greece. Plans were changed, however, due to developments in neighboring Yugoslavia. The Yugoslav government had signed the Tripartite Pact on 25 March, only to be overthrown two days later by a British-encouraged coup. Hitler viewed the new regime as hostile and immediately decided to eliminate it. On 6 April Germany simultaneously invaded both Yugoslavia and Greece, making rapid progress and forcing both nations to surrender within the month. The British were driven from the Balkans after Germany conquered the Greek island of Crete by the end of May.Although the Axis victory was swift, bitter partisan warfare subsequently broke out against the Axis occupation of Yugoslavia, which continued until the end of the war.
The Allies did have some successes during this time. In the Middle East, Commonwealth forces first quashed an uprising in Iraq which had been supported by German aircraft from bases within Vichy-controlled Syria, then, with the assistance of the Free French, invaded Syria and Lebanon to prevent further such occurrences.