The peace settlement that was signed at Versailles in 1919, at the end of the First World War, imposed very harsh terms against Germany. Germany was blamed for causing the war, and France had been a primary victim, with much of the war's battlefront being fought on French soil. American president Woodrow Wilson had wanted a resolution to the conflict that would be more focused on building future peace between nations. France, however, felt deeply wronged and wanted Germany to be punished as an aggressor. Great Britain tended to support France's position.
As a result, the Treaty of Versailles, which came out of the Paris Peace Conference in 1919, was very punitive towards Germany. Germany was forced to admit responsibility for causing the Great War (World War I). We now call that "the war guilt" clause of the treaty. Germany also was forced to pay large reparation payments to the Allies (who opposed Germany in the war). The German economy and national pride were deeply affected by this. On top of that, the Great Depression (which was a global phenomenon) became worse in Germany than in America. The bad situation in Germany made it possible for a radical leader like Hitler, making all sorts of bold promises, to win over enough people to rise to power. So the Versailles treaty's attempt to punish Germany backfired, and actually led to a second, even more deadly Second World War.
