Hi! More answers are welcome, but fyi, there have been some enthusiastically thorough responses on this question before, so check these out:

• If Nazi Germany was the Third Reich, what were the First and Second Reich? - featuring /u/astrogator and /u/kieslowskifan

• We've all heard of the Third Riech, but what about the Second Reich, and First Riech? - by /u/KanzlerAndreas