>почему американцы индейцев несколько веков не трогали, а
>отгеноцидили их только в 19 веке.

феерический бред, кстати
https://en.wikipedia.org/wiki/Siege_of_Fort_Pitt
https://en.wikipedia.org/wiki/Native_American_disease_and_epidemics#Impact_on_population_numbers

For Commander-in-Chief, North America Jeffery Amherst, who
before the war had dismissed the possibility that the
Indians would offer any effective resistance to British
rule, the military situation over the summer had become
increasingly grim. The frustration was so great, he wrote
to Colonel Henry Bouquet and instructed him not to take
any Indian prisoners. He proposed that they should be
intentionally exposed to smallpox, hunted down with dogs,
and "Every other method that can serve to Extirpate this
Execrable Race."

в северной америке в 17-18 веке убили, по разным оценкам,
до 20 миллионов индейцев (в основном через оспенные
одеяла и все такое), к 1800-му году их оставалось
только 600,000, к 1900-му 250,000 - это, в принципе,
естественная убыль от потери привычных мест обитания.