How might events in Europe have been different if European leaders had not decided to pursue an appeasement policy toward Hitler?

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.