This is a timeline of events of World War II in 1939, from the start of the war on 1 September 1939. For events preceding September 1, 1939, see the timeline of events preceding World War II.
Nazi Germany's invasion of Poland on 1 September 1939, and Britain and France's declaration of war on Germany two days later marks the beginning of World War II. After the declaration of war, western Europe saw very little land or air active military confrontation at first, and the period was termed the "Phoney War". In eastern Europe, however, the agreement between the Soviet Union and Nazi Germany signed on 23 August opened the way in September for the Soviet Union's invasion of eastern Poland, which was divided between the two invaders before the end of the month. The Soviet Union starts a new military offensive by invading Finland at the end of November.