Following Hitler's failed bid to take power in Munich, how did he vow he would take power in Germany?

He vowed that he will gain power through political means, which at the end happened. Namely, after he left the prison, he became the leader of Nazi party, which at the elections gained more supporters.

Explanation:

Hitler was inspired by Mussolini's March on Rome, believing that he and his followers could do the same in Germany. Still as he failed, he was sent to prison. There, he started creating his political platform, that will lead him to gaining full authority in the country.