The event widely recognized as the beginning of World War II was the German invasion of Poland on September 1, 1939. This act of aggression marked the failure of appeasement policies in Europe and triggered a rapid response from Britain and France, who declared war on Germany shortly thereafter. The invasion was characterized by the use of Blitzkrieg tactics, which emphasized swift and coordinated attacks combining air power and ground forces. This invasion set off a chain reaction of warfare, leading to a global conflict that would last until 1945, involving numerous nations and resulting in widespread destruction and loss of life.