The major causes of World War II were numerous. They include the impact of the Treaty of Versailles following WWI, the worldwide economic depression, failure of appeasement, the rise of militarism in Germany and Japan, and the failure of the League of Nations. ... Then, on September 1, 1939, German troops invaded Poland.
World War II was one of the transformative events of the 20th century, causing the death of 3 percent of the world's population. Deaths in Europe totaled 39 million people — half of them civilians. Six years of ground battles and bombing resulted in widespread destruction of homes and physical capital.
