Final answer:
The Nazi Party's central belief was racial purity and the supremacy of the Aryan race, as dictated by Hitler's manifesto, Mein Kampf, leading to discrimination and the Holocaust.
Step-by-step explanation:
A central belief the Nazi party fanatically held was the notion of racial purity and the supremacy of the so-called Aryan race. This ideology was deeply rooted in anti-Semitism and the belief that Aryans, particularly Germans, were a master race destined to dominate others. Nazi philosophy was codified in Adolf Hitler's manifesto, Mein Kampf, which outlined a worldview where races were ranked hierarchically, with Jews and Slavs considered inferior and dangerous to the purity and success of the Aryan race. This racial ideology justified policies of extreme discrimination, aggression, and eventually led to the systematic extermination of millions in the Holocaust, the worst genocide in human history.