The event recognized as the beginning of World War II is the invasion of Poland by Germany on September 1, 1939. This aggressive act marked the culmination of various territorial ambitions by Adolf Hitler and the Nazi regime. Following the invasion, Britain and France declared war on Germany on September 3, 1939, thus formally initiating the conflict. Germany's invasion of Poland not only swiftly resulted in the capture of Warsaw but also showcased the devastating military tactics of Blitzkrieg, which combined fast-moving ground forces with air support. This invasion set off a series of events that would lead to a global conflict, shaping the course of 20th-century history.