"In all of human history"? Are you sure? Ghenghis Khan and Alexander the Great likely killed more people than either Hitler or Stalin.

And then there's the institution of slavery, which wasn't political until abolition efforts were underway. (Semi-related: hard to label abolitionists conservatives or rightists.)

It also bears mentioning that Hitler was anti-immigrant and nativist, which are the forces that animate today's Western conservative backlashes (including Trumpism).