Answer:
Because of the lack of US involvement in the world matters, the rising tensions in the world and because of the inaction and lack of willingness to deal with the problems
The League of Nations were formed shortly after the end of WWI and the United States went back to the policy of isolationism and the allies adopted a policy of appeasement and neutrality which further gave the impression that it was allowed to do whatever they wanted.
The assassination of Arch Duke France Ferdinand.
The Supreme Court can review and determine whether law are constitutional or unconstitutional.
