September 3 1939

Answer 1

France and Britain declared war on Germany in response to the invasion of Poland

Answer 2

Poland, Britain, and France declare war on Germany.

Answer 3

In respect to World War II, the date of September 3, 1939, is significant because it represents the formal start of hostilities between Germany, on the one hand, and, on the other, France and Great Britain. On September 3rd, the two Western Allies declared war on Germany, the forces of which were by then already invading Poland.