Why did the holocoaust happen?

Because Hitler needed a scapegoat for the people and his thugs to rally against so he picked out the Jews because not they tended to stand apart from the rest and a proportion of them had accrued some wealth to steal. they also went for Gipsy's catholics people with disability people that had a hint of Jewish background and anyone else that got in their way. Most of this would probably have been forgotten by now but for the fact that the world Jewish community has gone to great pains to to remind us of the Jewish victims of this period.