1. The Treaty of Versailles, which came out of the Paris Peace Conference, was very punitive towards Germany. Germany was forced to admit responsibility for causing the Great War (World War I) -- what we now call "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 wounded. The Great Depression was 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.
2. The Paris Peace Conference did not give Arab peoples the full self-determination that Woodrow Wilson's "14 Points" ideas would have hoped. They were placed under "mandate" governments, with European powers (Britain and France) serving in governing positions in the Middle East. The history of many of today's issues in the Arab world as well as the Israel / Palestine conflict are rooted in what happened in the settlements and arrangements made after World War I.