Earlier quoted context omitted.
The Europeans didn't topple any empire in the Americas. They collapsed by themselves due to the sickness brought over by the Europeans before they made contact. It would have been logistically impossible to topple an empire overseas.
This sounds the same to me as saying: "The gunshot didn't kill him. The infection did."
Imagine a hit man showing up to work one day, only to find his targets already dead along with their entire town... and only much later finds out that it's because he'd been an asymptomatic carrier for weird space germs when he was casing the joint the previous month.