There are a number of factors which explain why Hitler became chancellor in January 1933. However, any of the factors, on their own, would not have individually resulted in his appointment. They are all linked in a web of causation and if any of the factors were missing, Hitler may well have not been appointed chancellor.
However, through saying this I feel that one of the most important factors as to why Hitler was appointed in 1933, was the depression, which then leads to the key factor of the Nazis electoral success. The depression derived from the Wall Street Crash, when people rushed to sell their shares because they realised the companies were doing badly. Thousands of businesses and people were ruined. This affected Germany because America withdrew its loans and the German economy collapsed. Millions were left unemployed. The new Weimar government broke down and people were ready to listen to groups like Hitler's Nazis, who promised a strong government and a better way of life.
People who had never been interested in politics before found themselves listening to extremist groups because the government had collapsed -'Bad times for the Weimar Republic were good times for the Nazis and other extremist groups'. The depression was a tremendous piece of good luck for the Nazis, because it enabled them to win the largest proportion of voted cast, meaning that Hitler was knocking on the door of Hidenburg asking for the chancellorship.
However, it was only after the actions of Franz Von Papen, the previous chancellor of 1932, that Hidenburg felt he could trust Hitler in power (as the chancellor). As Von Papen was replaced by general Schleicher in December 1932 he was outraged, especially as they was some what of a ongoing conflict between the two. Therefore, Von Papen...