On this day in 1939, German forces under the control of Adolf Hitler bombard Poland on land and from the air. Germany invades Poland. September 1, 1939 Germany invades Poland, initiating World War II in Europe. This time, Britain and France could no longer ignore Germany’s actions and declared war on Germany on September 3rd 1939. Germany invaded Poland on 1st September 1939 and just three weeks later on September 28th 1939 Poland surrendered entirely. German Invasion of Poland (September 1, 1939-October 6, 1939)--Germany invaded Poland on September 1, and Britain, France, and Canada, declared war on Germany on September 3. World War II had begun. German forces broke through Polish defenses along the border and quickly advanced on Warsaw, the Polish capital. The Soviet Union joined the war on Germany's side on September 17, with the Soviet Invasion of Poland … Why did Germany invade Poland? All of the British leaders claimed that the entire responsibility for starting the war was Hitler’s. Germany decided to invade Poland on September 1, 1939. Hundreds of thousands of refugees, both Jewish and non-Jewish, fled the German advance hoping the Polish army could halt the German advance. Prime Minister Chamberlain broadcast that evening on British radio that “the responsibility for this terrible catastrophe (war in Poland) lies on the shoulders of one man, the German Chancellor.”