Why did Germans at first support Hitler?
He promised the bring Germany back to its glory days.
One of the biggest issues that Germany was facing post-WWI is their economy. Their currency was so worthless after WWI that there are pictures of children playing with stacks of it in the streets. Some people today in Germany doing renovations on their homes sometimes discover that people used the currency as wallpaper back then. Hitler promised to revitalize Germany's economy and bring back the days when Germany was a economic and political powerhouse in Europe. He was able to garner support because he was able to scapegoat the Jewish community as the problem for their difficulties (which is obviously ridiculous and anti-semitic).
The reason many people still supported him well into the war was because he did deliver on some of his early promises. Historians will say that in early 1930's Germany, feelings were good. Hitler rebuilt German town, roads, built resorts and sent thousands of families on vacation, led the creation of a "People's Car" that anyone could afford. That very car was an early form of the VW Beetle. Meanwhile he was secretly rebuilding Germany's arms (a violation of the Versailles Treaty).
Germany wasn't alone in the rise of nationalism and ethnocentrism. Many European countries faced the rise of these types of groups. These types of groups even took power in many countries. From small legislative seats, to even the Chancellor (or their version of president).