The global conflict precipitated by the invasion of Poland in 1939 was World War II. On September 1, 1939, Nazi Germany, led by Adolf Hitler, invaded Poland, marking the beginning of the war in Europe. This invasion prompted Britain and France to declare war on Germany on September 3, 1939, thereby expanding the conflict. The invasion employed Blitzkrieg tactics, emphasizing rapid, coordinated assaults that overwhelmed Polish defenses. This act of aggression underscored the failure of appeasement policies and revealed the expansionist ambitions of totalitarian regimes. World War II would ultimately involve numerous nations and result in unprecedented destruction and loss of life.