If the U.S. would not have intervened the entirety of Europe would have been conquered by Hitler. He was very close to doing so. Russia, no. Europe, very well could have. Japan was not supposed to attack the U.S. We stayed out of the war because we were in a horrible recession and basically could not go to war. Hitler was very close to gaining massive amounts of power. We won World War 2 simply by outnumbering him. Between Germany, Japan, and Italy they were one of the strongest forces to have ever been reckoned with. The Holocaust was not just a horrible genocide, it was also the story of a man that damn near held the world in his hands. We stepped in at the last minute with our dick in our hands because we knew Hitler would not stop until he kicked all of Europes ass or had other countries join him out of fear. Russia had no intention of conquering Germany. Germany couldn't beat Russia simply because of a bunch of fucking snow. Meanwhile Stalin exterminated anybody that wasn't an atheist and not a part of his extremist agenda. Austria surrendered without a single shot fired. It would not had been long until other nations followed suit. Brush up on your history bro.