My understanding is that after WW1 the US became isolationist because we lost a lot of lives in WW1 and the world did not get better (WW1 was proclaimed the war to end all wars).
The Allies won largely because of the Americans joining the fight. The Germans had settled with Russia so could concentrate their forces on the Western front, except there now were lots of Americans on the Allied side.
Woodrow Wilson put forward 14 points for a fair peace. The Allies ignored all but one that established a League of Nations and we know how that turned out. The result was an unstable Germany and the eventual rise of a madman. With strong isolationist sentiments the US largely stayed out the war until Japan attacked.
What is the parallel today? I'm not sure except that the Iranian govt is Hitler level of evil. If we follow the Obama doctrine of fake red lines, evil would have nuclear bombs. Tump is doing something different. I hope Trump is right.