Why did the world war ll begin and why?

Like any major war, World War II did not have a specific start date but was the result of a 20 year buildup of resentment over the outcome of the First World War (know then as The Great War); however, 1939 is condsidered to be the year when this resentment by Germany, Italy and Japan, of territory allotments and power, reached war status.

The Great War (World War I) reduced Germany to a powerless and very restricted and confined nation, yet two of the victors, Japan and Italy, also felt slighted. They felt that the United States, Great Britain and France treated themselves to the lion's share of the territorial spoils and power, leaving the others little to pay for their war efforts.