[chrisco255]

I believe small pox was the major one, I've heard among the Incas for example, it wiped out between 60 and 90 percent of the population. The main reason the colonists were able to spread so easily in the two continents is because disease wiped out huge swaths of the native population before many settlers even arrived. It's not like muskets are all that superior to bow and arrow (if at all, due to reload speed). Much of the land was just left vacant and unoccupied, and former cities abandoned.

[atomi]

And then came Colt's Revolver.

> A Texas Ranger, Captain Samuel Walker, wrote Colt a testimonial that read, in part:"Your pistols...[are] the most perfect weapon in the World... to keep the various warlike tribes of Indians and marauding Mexicans in subjection."

https://www.pbs.org/wgbh/theymadeamerica/whomade/colt_hi.htm...

[inglor_cz]

The 20th century decolonization wars showed that natives can adapt to modern weaponry fairly well.

But you need the numbers to pull this off. Sioux are not numerous enough to threaten American dominance of their territory. If they were as numerous as, say, Punjabis, that would be a different story.

[selimthegrim]

Punjabis acquitted themselves fairly well in 1849.