The Treaty of Versailles is the document that ends World War I.In this treaty, Germany is forced to take full responsibility for World War I and must pay reparations to countries like France and Britain. This ultimately ruins the Germany economy and allows for the rise of Hitler.
The Marshall Plan is put into place after World War II. This plan gives $13 billion worth of economic aid to Western European countries whose economy's are struggling after World War II. The ultimate goal of this plan (implemented by the US federal government) is to ensure that these Western European countries do not fall under the control of the Soviet Union and their communist system.
President Wilson’s proposal to form the League of Nations was most weakened by isolationist sentiment in the US, which was filled with people who thought joining the League of Nations would result in the US getting dragged into more wars.
"The United States withdrew its support." was perhaps the most immediate result of Diem's refusal to hold elections, but it should be noted there were others as well.
You didn't include options but here's the jist - there were many casualties, cities and towns were left in ruins, national identities across Europe were in shambles.
