Germany invaded Poland on September 1, 1939, marking the beginning of World War II. The invasion began with a surprise attack by German forces at dawn, including the shelling of Polish fortifications at the Baltic port of Danzig by the German battleship Schleswig-Holstein. The German assault came from multiple directions, with Army Group North attacking from Pomerania and East Prussia, and Army Group South advancing from Silesia and Slovakia. The campaign lasted until October 5-6, 1939, when Poland was defeated and subsequently divided between Germany and the Soviet Union as per their agreement. This invasion led Britain and France to declare war on Germany on September 3, 1939.