In response, Britain and France declared war on Germany two days later, on September 3, 1939.
A number of factors led up to this conflict, including:
- The rise of Adolf Hitler and the Nazi Party in Germany in the 1930s.
- Hitler's aggressive foreign policy, which included the remilitarization of the Rhineland in 1936, the annexation of Austria in 1938, and the occupation of Czechoslovakia in 1939.
- The desire of Britain and France to maintain the balance of power in Europe and prevent Germany from becoming too powerful.
- The failure of the League of Nations, an international organization created after World War I to promote peace, to prevent the outbreak of war.