Causes of World War II

Proximate Causes

Nazi Dictatorship

Adolf Hitler in Bad Godesberg, Germany, 1938

Hitler and his Nazis took full control of Germany in 1933–34 (Machtergreifung), turning it into a dictatorship with a highly hostile outlook toward the Treaty of Versailles and Jews. It solved its unemployment crisis by heavy military spending.

Hitler's diplomatic tactics were to make seemingly-reasonable demands and to threaten war if they were not met. After concessions were made, he accepted them and moved onto a new demand. When opponents tried to appease him, he accepted the gains that were offered and went to the next target.

That aggressive strategy worked as Germany pulled out of the League of Nations (1933), rejected the Versailles Treaty, began to rearm with the Anglo-German Naval Agreement (1935), won back the Saar (1935), re-militarized the Rhineland (1936), formed an alliance ("axis") with Mussolini's Italy (1936), sent massive military aid to Franco in the Spanish Civil War (1936–39), seized Austria (1938), took over Czechoslovakia after the British and French appeasement of the Munich Agreement of 1938, formed a peace pact with Stalin's Russia in August 1939 and finally invaded Poland in September 1939.

Remilitarization of the Rhineland

In violation of the Treaty of Versailles and the spirit of the Locarno Pact and the Stresa Front, Germany remilitarized the Rhineland on March 7, 1936, by moving German troops into the part of western Germany in which according to the Versailles Treaty, they were not allowed. Neither France nor Britain was prepared fight a preventive war to stop the violation and so there were no consequences.

Italian Invasion of Abyssinia

Following the Stresa Conference and even as a reaction to the Anglo-German Naval Agreement, the Italian dictator Benito Mussolini attempted to expand the Italian Empire in Africa by invading the Ethiopian Empire, also known as the Abyssinian Empire. The League of Nations declared Italy to be the aggressor and imposed sanctions on oil sales, which proved ineffective.

Italy annexed Ethiopia in May 1936 and merged Ethiopia, Eritrea and Somaliland into a single colony, known as Italian East Africa. On June 30, 1936, Ethiopian Emperor Haile Selassie gave a stirring speech before the League of Nations denouncing Italy's actions and criticizing the world community for standing by. He warned, "It is us today. It will be you tomorrow". As a result of the League's condemnation of Italy, Mussolini declared the country's withdrawal from the organization.

Spanish Civil War

Francisco Franco and Heinrich Himmler in Madrid, Spain, 1940

Between 1936 and 1939, Germany and Italy lent support to the Nationalists led by general Francisco Franco in Spain, and the Soviet Union supported the existing democratically-elected government, the Spanish Republic, led by Manuel Azaña. Both sides experimented with new weapons and tactics. The League of Nations was never involved, and its major powers remained neutral and tried with little success to stop arms shipments into Spain. The Nationalists eventually defeated the Republicans in 1939.

Spain negotiated with joining the Axis but remained neutral during World War II and did business with both sides. It also sent a volunteer unit to help the Germans against the Soviets. The Spanish Civil War was considered in the 1940s and 1950s to be a prelude to World War II, which was the case to some extent by changing it into an antifascist contest after 1941, but bore no resemblance to the war that started in 1939 and had no major role in causing it.

Second Sino-Japanese War

In 1931, Japan took advantage of China's weakness in the Warlord Era and fabricated the Mukden Incident in 1931 to set up the puppet state of Manchukuo in Manchuria, with Emperor Puyi, who had been the last emperor of China. In 1937 the Marco Polo Bridge Incident triggered the Second Sino-Japanese War.

The invasion was launched by the bombing of many cities such as Shanghai, Nanjing and Guangzhou. The latest, which began on 22 and 23 September 1937, called forth widespread protests culminating in a resolution by the Far Eastern Advisory Committee of the League of Nations. The Imperial Japanese Army captured the Chinese capital city of Nanjing and committed war crimes in the Nanjing Massacre. The war tied down large numbers of Chinese soldiers and so Japan set up three different Chinese puppet states to enlist some Chinese support.

Anschluss

Cheering crowds greet the Nazis in Innsbruck

The Anschluss was the 1938 annexation by threat of force of Austria into Germany. Historically, Pan-Germanism was the idea of creating a Greater Germany to include all ethnic Germans into one nation-state and was popular in both Austria and Germany.

The National Socialist Program included the idea in one of its points: "We demand the unification of all Germans in the Greater Germany on the basis of the people's right to self-determination".

The Stresa Front of 1935 between Britain, France and Italy had guaranteed the independence of Austria, but after the creation of the Rome-Berlin Axis, Mussolini was much less interested in upholding its independence.

The Austrian government resisted as long as possible but had no outside support and finally gave in to Hitler's fiery demands. No fighting occurred, most Austrians supported the annexation and Austria was fully absorbed as part of Germany. Outside powers did nothing, and Italy had little reason for continued opposition to Germany and, if anything, was drawn in closer to the Nazis.

Munich Agreement

The Sudetenland was a predominantly-German region in Czechoslovakia along the border with Germany. It had more than three million ethnic Germans, who comprised almost a quarter of the country's population. In the Treaty of Versailles, the region was given to the Czechoslovakia against the wishes of most of the local population. The decision to disregard its right to self-determination was based on France's intent to weaken Germany. Much of Sudetenland was industrialised.

British Prime Minister Neville Chamberlain and Hitler at a meeting in Germany on 24 September 1938, and Hitler demanded the immediate annexation of Czechoslovak border areas.

Czechoslovakia had a modern army of 38 divisions, backed by a well-noted armament industry (Škoda) and military alliances with France and the Soviet Union. However, its defensive strategy against Germany was based on the mountains of the Sudetenland.

Hitler pressed for the Sudetenland's incorporation into Germany and supported German separatist groups within the region. Alleged Czechoslovak brutality and persecution under Prague helped to stir up nationalist tendencies, as did the Nazi press. After the Anschluss, all German parties except for the German Social-Democratic Party merged with the Sudeten German Party (SdP). Paramilitary activity and extremist violence peaked during the period, and the Czechoslovak government declared martial law in parts of the Sudetenland to maintain order. That only complicated the situation, especially since Slovak nationalism was rising from suspicion towards Prague and encouragement by Germany. Citing the need to protect the Germans in Czechoslovakia, Germany requested the immediate annexation of the Sudetenland.

In the Munich Agreement on September 30, 1938, the British, French, and Italian prime ministers appeased Hitler by giving him what he wanted in the hope that it would be his last demand. The powers allowed Germany to move troops into the region and incorporate it into the Reich "for the sake of peace". In exchange, Hitler gave his word that Germany would make no further territorial claims in Europe.

Czechoslovakia was not allowed to participate in the conference. When the French and British negotiators informed the Czechoslovak representatives about the agreement and that if Czechoslovakia would not accept it, France and Britain would consider Czechoslovakia to be responsible for war and stay neutral, Czechoslovak President Edvard Beneš capitulated and Germany took the Sudetenland unopposed.

Chamberlain's policies have been the subject of intense debate for more than 70 years by academics, politicians and diplomats. The historians' assessments have ranged from condemnation for allowing Hitler's Germany to grow too strong to the judgment that Germany was so strong that it might well win a war and so the postponement of a showdown was in the country's best interests.

German Occupation and Slovak Independence

All territories taken from Czechoslovakia by its neighbours in October 1938 ("Munich Dictate") and March 1939

In March 1939, breaking the Munich Agreement, German troops invaded Prague, and with the Slovaks declaring independence, Czechoslovakia disappeared as a country. The entire ordeal ended the French and British policy of appeasement.

Italian Invasion of Albania

After the German occupation of Czechoslovakia, Mussolini feared for Italy becoming a second-rate member of the Axis. Rome delivered Tirana an ultimatum on March 25, 1939, by demanding the accession to Italy's occupation of Albania. King Zog refused to accept money in exchange for allowing a full Italian takeover and colonization of Albania.

On April 7, 1939, Italian troops invaded Albania, which was occupied after a three-day campaign with minimal resistance offered by Albanian forces.

Soviet–Japanese Border War

In 1939, the Japanese attacked west from Manchuria into the Mongolian People's Republic after the 1938 Battle of Lake Khasan. They were decisively beaten by Soviet units, under General Georgy Zhukov. After the battle, the Soviet Union and Japan were at peace until 1945. Japan looked south to expand its empire, which led to conflict with the United States over the Philippines and the control of shipping lanes to the Dutch East Indies. The Soviet Union focused on its western border but left 1 million to 1.5 million troops to guard its border with Japan.

Danzig Crisis

The Polish Corridor and the Free City of Danzig

After the end of Czechoslovakia proved that Germany could not be trusted, Britain and France decided on a change of strategy. They decided any further unilateral German expansion would be met by force. The natural next target for German expansion was Poland, whose access to the Baltic sea had been carved out of West Prussia by the Versailles Treaty, which made East Prussia an exclave. The main port of the area, Danzig, had been made into a free city-state under Polish influence guaranteed by the League of Nations, a stark reminder to German nationalists of the Napoleonic free city that had been established after French Emperor Napoleon I's crushing victory over Prussia in 1807.

After taking power, the Nazi government made efforts to establish friendly relations with Poland, which resulted in the signing of the ten-year German–Polish Non-Aggression Pact with the Piłsudski regime in 1934. In 1938, Poland participated in the dismemberment of Czechoslovakia by annexing Zaolzie. In 1939, Hitler claimed extraterritoriality for the Reichsautobahn Berlin-Königsberg and a change in Danzig's status in exchange for promises of territory in Poland's neighbours and a 25-year extension of the non-aggression pact. Poland refused for fear of losing its de facto access to the sea, subjugation as a German satellite state or client state and future further German demands. In August 1939, Hitler delivered an ultimatum to Poland on Danzig's status.

Polish Alliance with Entente

In March 1939, Britain and France guaranteed the independence of Poland. Hitler's claims in the summer of 1939 on Danzig and the Polish Corridor provoked yet another international crisis. On August 25, Britain signed the Polish-British Common Defence Pact.

Molotov–Ribbentrop Pact

Germany invaded Poland on 1 September 1939 which directly led to the Anglo-French declaration of war on Germany on 3 September. The Soviet Union joined Germany's invasion of Poland on 17 September.

Nominally, the Molotov–Ribbentrop Pact was a non-aggression treaty between Germany and the Soviet Union and was signed in Moscow on August 23, 1939, by Soviet Foreign Minister Vyacheslav Molotov and German Foreign Minister Joachim von Ribbentrop.

In 1939, neither Germany nor the Soviet Union was ready to go to war with each other. The Soviet Union had lost territory to Poland in 1920. Although officially called a "non-aggression treaty," the pact included a secret protocol in which the independent countries of Finland, Estonia, Latvia, Lithuania, Poland and Romania were divided into spheres of interest between both the parties. The secret protocol explicitly assumed "territorial and political rearrangements" in those areas.

All of the mentioned countries were invaded, occupied, or forced to cede part of their territory by the Soviet Union, Germany or both. Finland and Romania maintained their independence, however being forced to cede parts of their territory.

The conflict between the Soviet Union and Finland had a great impact of assessing the former's military capabilities by Nazi Germany.