Look at population growth. Global population growth spiked with the dawn of the industrial revolution.
Before that global population started an upward trend in the middle of the 14th century following the black death. At the time there were an estimated 350-400 million people on the planet. We know that the bulk of that population existed in the Ancient world in Africa, Asia, and Europe.
The idea that there were even 100 million people available to kill in the Americas a mere 100 years later is just laughably absurd. 100% complete genocide of both continents before the Europeans came on board won't get you to 100 million.