At least 20 world leaders gathered Tuesday in Poland to commemorate the start of World War II 70 years ago -- a conflict in which 6 million Poles died. Germany's pre-dawn invasion began when the battleship Schleswig-Holstein fired on the Westerplatte military base in Gdansk harbor on September 1, 1939. The attack set off a chain of events that eventually embroiled all of the world's major powers in the war.
