World War II started when Germany invaded which country?
World War II officially started when Germany invaded Poland.
The German invasion began on September 1, 1939, initiating the global conflict. Germany employed a new military tactic known as Blitzkrieg (“lightning war”), which utilized fast-moving armored divisions supported by air power to overwhelm Polish defenses quickly. Following this act of aggression, Great Britain and France, honoring their treaties with Poland, issued an ultimatum to Germany demanding a withdrawal. When Germany refused, both nations declared war on Germany on September 3, 1939, formally commencing World War II.
Source:
https://www.youtube.com/watch?v=RZ_iboV6ZwE
https://www.threads.com/@beliproduk.official/post/DSBdOi4kp2J