The Treaty of Versiaisles
What Gave Hitler Power
The Night of The Long Knives
Hitler started resenting his political parties and "convinced" (forced) them to die.This brought in an overthrow of the government which brought the Nazi party into power.
There was more than this that gave power to Hitler he also passed an act; "The Enabling Act" which stated that the government could pass laws without approval of the parliament. This act almost gave full power to Hitler. We say almost because of the fact that there could still be multiple political parties in Germany so on July 14 1933 Hitler declared the Nazi party as the only legal party, which gave full power to Adolf Hitler.
Actions Hitler Took
Ruth Henig (2013). Versailles and After, 1919-1933. Routledge. p. 17