World War 2 By lpereira24357 Sep 1, 1939 1939 September 1 Germany invades Poland. World War II begins. Period: Sep 1, 1939 to Sep 2, 1945 World War 2 1939 September 1 1945 September 2 Sep 3, 1939 1939 September 3 France and Great Britain declare war on Germany.