I need help.... How did the Allies act passively at the onset of German aggression under Hitler? Why?

Answer 1

The League of Nations' response to German aggression under Hitler was famously, one of so-called "appeasement", which means that they hoped to avoid conflict by letting Hitler "get away with" certain violations of the Treaty of Versailles.

For example, when Hitler started openly flaunting his extensive re-arming of the German military (in direct violation of the treaty), the League of Nations thought that they could avoid direct conflict by not "overreacting" - at this point in time, most in positions of power throughout the world still considered Hitler to be a joke. However, Hitler was only emboldened by this appeasement, but started ramping up his actions.

The other drastic failures on the part of the League of Nations had not to do with appeasement, but with major players like Britain and France actively engaging in negotiation and making concessions with Germany. The British officially agreed with Germany that they should be allowed to have at least a fraction of their former navy, and the French took zero action when the Germans began to re-militarize the Rhineland (citing German national safety due to recent alliances with France and Russia).

Obviously, the refusal to take Hitler seriously was a major mistake that the League of Nations came to deeply regret.