How World War 2 happened?

Answer 1

Hitler kept expanding and British and french got mad. Hitler wanted more territory and those of German ethnicity to be within the German state so he started claiming land where those people lived and that had been part of the 2nd Reich (the German Empire under the Kaiser). The world had was recovering from the Great Depression at the time so the allies stalled Hitler by giving him what he wanted, this was called appeasement and led to Czechoslovakia being carved up between surrounding states.

Hitler knew his army was strong enough to take land now and so it invaded Poland, which Britain had sworn to defend in the event of German aggression. this lead to a British and French ultimatum and when that ended with no withdrawl by Hitler British and French Prime Ministers formally declared war on nazi Germany.