How did different languages/ethnicity get their naming? Why isn't it standardized?

by breakathon

I'm curious as to how the different names for languages/ethnicity arose, and why there really isn't a standard. In a sense:

America - Americans

Italy - Italians

China - Chinese

Germany - Germans

France - French

England -English

Why do some of them like France, simply go to French? Why not Francen...or Francese or something (Granted, they both sound extraordinarily awkward now, but thats likely due to never being used). Why is Germany German, not Germanese? Not exactly these specifically, but in general how did each language get its word?

Comrade-Chernov

This probably would be better on /r/linguistics as it has more to do with how language developed over time to refer to certain peoples rather than standardized demonyms.