It's the opposite of the butterfly effect, he's more likely arguing that WW2 was built on the frustrations and ideologies thrust forth as a result of WW1, so merely killing one angry officer isn't necessarily going to avoid one or another catastrophe involving war and genocide. WW2 might in fact have been unavoidable (not sure whether this is true or not, but it might be). Some other racist charismatic dude might just take his place, ready to harness whatever ill will there was around him/her. (Well, probably "him".)