1) During the late 1800s and early 1900s, European nations engaged in imperialism by colonizing parts of Africa, Asia, and the Pacific which led to tensions between countries and contributed to World War I and II. 2) By the 1900s, nationalism was on the rise in Europe as people took great pride in their countries, but this strong sense of nationalism also caused conflicts between nations. 3) To protect themselves from each other, European countries formed military alliances that ultimately divided them into two major alliance groups prior to both World War I and II.