What has always baffled me is why so many Germans supported Adolf Hitler who preached German nationalism but was not a German by birth, he was an Austrian who only became a German citizen in 1932 less than a year before he came to power as Chancellor of Germany in 1933. Why was it not an issue for Germans?
This answer by /u/HighschoolCommissar might help you understand this.
Hitler considered himself German. He fought for Germany in WW1 and came from the ethnically German speaking part of Austria-Hungary.
Additionally, consider this answer Did Hitler's Austrian origins cause him any political issues or become a point of any major opposition movement during his rise to power in Germany? written by u/kieslowskifan