The Holocaust happened primarily due to the extreme antisemitic ideology of the Nazi regime, led by Adolf Hitler, which falsely portrayed Jews as a dangerous race threatening the purity and well-being of the so-called "Aryan" German race. This racism was combined with nationalist, political, and social factors including long-standing European antisemitism, post-World War I instability, and Nazi state policies that systematically excluded, persecuted, and eventually sought to exterminate Jews across Europe. The causes involved a complex mix of ideology and opportunism: extreme racist antisemitism provided the ideological basis, but many different motivations such as individual and institutional gains, coercion, and competition between Nazi government departments also played a role in expanding and implementing the genocide. The Holocaust was not a spontaneous event but the result of years of growing hate and a series of radical decisions, only fully taking the shape of mass murder during World War II after Nazi territorial expansion brought millions more Jews under their control.

In summary, the Holocaust was caused by a unique convergence of virulent antisemitism, Nazi racial ideology, the political context of interwar Europe, and the functioning of the Nazi state machinery during wartime that made the systematic murder of six million Jews possible.