Isolationism caused WWII

The immediate cause of WWII was Adolf Hitler.  He wanted to refight WWI and win instead of losing.  Nobody else in Europe was that crazy, and nobody believed Hitler was that crazy.  Hitler started throwing Germany's weight around in the 1930s  If the two surviving great powers, Britain and France, had exerted them selves,  Hitler could have been stopped, deposed, brought before an international trial and executed in the 1930's.   They didn't, their voter's didn't want to, nobody wanted to risk getting sucked into another WWI, and Germany looked like a pretty tough nut.  If the British and the French had had solid American backing, they might have found the stones to act. 
   But the Americans were into "isolationism".  "Let Europe stew in it's own juice."  This pusillanimous attitude got started during WWI.  After the WWI, there was a great peace treaty, the treaty of Versailles. To enforce Versailles, the American president Wilson wanted to set up the League of Nations.  But when he brought the League of Nations treaty to the US senate, the isolationists opposed it and defeated it.  Later on, conspiracy theories of WWI were circulated, things like the war was instigated by arms makers ("the merchants of death") as a way to increase sales.   Needless to say, a lot of people were unsatisfied by the deals cut at Versailles.  The British and the French scarfed up a lot of loose colonial territory.  The Germans thought they had been shafted.  The British had promised Palestine to both the Jews and the Arabs. 
   Net result, America withdrew from world affairs.  When Hitler started throwing his weight around we did nothing.  The French and the British lacked the will and the strength to do anything.  We should have said "We won't stand for any backchat out of this two bit dictator.  If he steps one inch out of line, we plan to clobber him good."  But the political strength of the isolationists was so great that we did nothing, we let Hitler grow in strength until he brought the world down in flames. 
   This political season you can hear the isolationists rising up again in America.  "No boots on the ground."  The Iranian nuke deal.  "Leading from behind."   We need to oppose this, lest it touch off WWIII.