After World War I, ambitious, dictatorial governments with imperial, expansionist ambitions came to power in Germany, Italy and Japan. The world depression, which started in 1929, had increased social and economic instability, exacerbated national rivalries and pushed the masses towards acceptance of the promises of right-wing demagogues in these countries.
At first, these governments were tolerated by the Western democracies, which viewed them as bulwarks against the growing threat of Communism. At the same time, memories of the brutality of the First World War encouraged Britain, France and the United States to search for peace rather than further conflict.
Furthermore, the League of Nations, which was established soon after the end of World War I, was weakened by the refusal of the US to join the organisation and, as a result, was unable to enforce disarmament or prolonged peace.
During the 1930s the League proved unable to stop increasing violations of international treaties and successive acts of national aggression. In 1933 Adolf Hitler was elected president of Germany. After investing in the reconstruction of the Germany military, he illegally stationed troops in the Rhineland in 1936.
In the same year, Italian dictator, Benito Mussolini conquered Ethiopia. In March 1938, Germany annexed Austria and finally, in September 1938 the British and French policy of appeasement allowed Hitler's Germany to seize Sudetenland in Czechoslovakia.
Over the next year the pace of Germany and Italy's illegal acts of expansion increased. In March 1939 Hitler's troops marched into the rest of Czechoslovakia, and the following month Italy seized Albania. Britain and France attempted to roll back their policy of appeasement, by forming alliances with Turkey, Greece, Romania, and Poland, and speeding up rearmament.
However, the change in allied foreign policy came too late. In May 1939 Germany and Italy signed a full military alliance. In August 1939 the signing of a non-aggression pact between Germany and the Soviet Union removed Hitler's fear of the possibility of war on two fronts.
As a result, World War II began on 1 September 1939, when Germany invaded Poland. Two days later, Britain and France declared war on Germany.