How and why did the Holocaust begin?

Historians generally feel that the beginning of the Holocaust was the date that Adolf Hitler was appointed chancellor of Germany (January 30, 1933). This is a compelling argument because much of the reason for the Nazi party's success was its propaganda against the communists and the Jews even before their ascendancy. The Germans were very desperate for a leader that could solve the economic hardships, particularly unemployment and inflation.  The state of desperation the Germans were facing allowed them to be convinced that the Jews were the root of all of their problems. There also was an element of fear in opposing the viewpoints of the Nazis.  
Hitler was able to turn the propaganda into law in September of 1935 with the Nuremberg Laws.  This anti-Jewish legislation established a firm legal ground on which to persecute the Jews in Germany.
 
 
https://www.jewishvirtuallibrary.org/an-introductory-history-of-the-holocaust