High Quality Content by WIKIPEDIA articles! This is a timeline of events that stretched over the period of World War II. For events preceding September 1, 1939, see the timeline of events preceding World War II. he Invasion of Poland, also known as the September Campaign or 1939 Defensive War in Poland and the Poland Campaign (German: Polenfeldzug) in Germany, was an invasion of Poland by Nazi Germany, the Soviet Union, and a small Slovak contingent that marked the start of World War II.