Your question has been up a couple weeks without an answer, perhaps due to its complexity. I'll answer at least part of it for you. For paragraph 4, I believe ultimately the verdict of history is that the Treaty of Versailles was a failure. Let me explain that, which also explains how it led to World War II.
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 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. Hitler promised a return to national greatness and fiercely rebuilt Germany as a military machine. The rise of Hitler and the Nazis brought about World War II in Europe.