The Weimar Republic (German: Weimarer Republik), officially the German Reich (Deutsches Reich), also referred to as the German Republic (Deutsche Republik), was the German federal state from 1918 to 1933. As a term, it is an unofficial historical designation that derives its name from the city of Weimar, where its constituent assembly first took place. The official name of the republic remained the German Reich as it had been during the German Empire because of the German tradition of sub-states.
The Reich was changed from a constitutional monarchy into a republic. In English, the country was usually known simply as Germany, and the Weimar Republic name became mainstream only in the 1930s.
Nazi Germany or the Third Reich, officially known as the German Reich until 1943 and Greater German Reich in 1943-45, was the German state between 1933 and 1945, when Adolf Hitler and the Nazi Party controlled the country which they transformed into a dictatorship. Under Hitler's rule, Germany quickly became a totalitarian state where nearly all aspects of life were controlled by the government. The Third Reich, meaning "Third Realm" or "Third Empire", alluded to the Nazis' conceit that Nazi Germany was the successor to the earlier Holy Roman Empire (800 - 1806) and German Empire (1871 - 1918). The Third Reich, which Hitler and the Nazis referred to as the Thousand Year Reich, ended in May 1945 after just 12 years, when the Allies defeated Germany, ending World War II in Europe.