The treaty ended WW1 and stated that Germany pay war reparations which then left Germany's economy ruined, they had limited military weapons and soldiers, and lost some of their land. This obviously made Germany mad Which led into WW2
Hitler and the Nazi Party
Japan wanted to expand into Southeast Asia and the Pacific. The U.S. demanded that Japan stop their expansion in Indonesia, Japan refused and the U.S. then deprived Japan of some of their goods which then led to war.
The Great Depression
Fascism is when a powerful dictator overthrows the government (or the government was already ruined and the dictators take over) and takes over total control of the economy, which usually isn't any better.
Germany had no government, no money, nothing. They were bankrupt and depressed and were desperate for help, so they supported Hitler and the Nazi Party. Hitler started to expand his empire into Austria, etc. And of course other powers felt threatened by him, especially because Hitler wanted to eliminate all Jews.
The Great Depression happened in the U.S. Their economy was suffering, just like Germany's. Only they didn't have a dictator in power. Most everyone was unemployed, but WW2 had pulled the U.S. out of their depression.
There was an important alliance formed in WW2, this alliance consisted of Germany, Italy, Japan, Hungary, Romania, and Bulgaria. This alliance was called the Axis powers. It was the Axis powers against the allies.