Downvoted but basically correct.

Difficult to pin something as all consuming as WW2 on "about" anything, but we can look at who fired the first shots, which was clearly the Japanese invasion of Manchuria in the east and the German invasion of Poland in the West (followed shortly after by the USSR invading Poland and later Finland from the other direction.)

It is not at all a given that, had Germany stayed within her international borders, that the Holocaust would have on its own triggered WW2. After all, mass murder in the Congo Free State didn't trigger invasion of Belgium.