This is a huge question because there are so many ways it could have turned out. Some possibilities that I can see:
- Hitler stays in power but doesn't take Austria or Czechoslovakia or Poland. He keeps rebuilding Germany until they actually are able to conquer all of Europe. So -- he doesn't start the war so early -- he builds his military but the Allies don't. He ends up winning WWII in the 1950s.
- Hitler falls from power because he can't expand Germany. The Holocaust never happens. Israel never comes to exist and the US is allied with Arab countries. You can argue that 9/11 never happens in this scenario.
- Hitler falls from power, WWII never happens. The US economy grows very slowly without the war to pull us out of the Depression. Technology doesn't progress so fast because the war doesn't force it to happen. The GI Bill never happens. America's standard of living is much lower than it is today.
Shoot, I got carried away and forgot that this is only about Europe... Okay, so that last one isn't so important but still interesting to me at least.
- Germany becomes a major power, but only about on the same level as France and England. WWII doesn't happen. Therefore, the Soviet Union doesn't take all of Eastern Europe. The Cold War never happens.
There are so many possibilities...
Adolph Hitler came in to power after his appointment from President Paul Von Hindenburg. He brought with him the idealism of a pure race in Germany and the expansion of Germany. Had other countries stepped in to stop Hitler early on instead of looking the other way, not anticipating his strength at being able to rally a population together in support of his causes, and the atrocities that he committed, there would not have been a World War II in Europe. The French would have had a stronger economy and France would have become a stronger world power. The most obvious of all is that the lives of so many Jewish people, Gypsies, Homosexuals, Jehovah Witnesses, and persons with disabilities would have been spared. In addition, the damages that occurred as the result of the war would have not occurred such as the demolition of cities. In turn the influx of immigrants to Germany and Europe after the war would not have been as significant because the extra labor would not have been needed to rebuild the cities.