It's interesting, a large portion of today's problems were caused by the treaties after the first and second world war. WWI placed Germany in dire straights, and was the cause of the European conflict.
After WWII, Russia was given a large swath of land, and Israel was created. Communism was later determined to be a problem for the free world, and the conflicts since WWII had been over communism or countries that were directly assisted by communist Russia; China, North Korea, Cuba, Vietnam, Iran, Afghanistan.