Hitler invaded Poland, rather than helping they decided to let him keep Poland to prevent starting another war.
The League of Nations The League of Nations was a committee of political representatives from different countries. This "league" had no real power as they could not declare war or pass laws. Germany and the United States were not part of the organization.
Treaty of Versailles The Treaty stated that Germany had to take responsiblity for causing the war and were forced to pay repreations for damages and was forced to give up a portion of their territory.