HELPING THE OTHERS REALIZE THE ADVANTAGES OF GAS PISTON AR PISTOL UPPER

Schmidtt's review(pdf) appears to exhibit a comparatively constant decline from the time of European contact till roughly the start with the 20th century (at which point their inhabitants started escalating again). The one bit in there that seriously sticks out like a sore thumb was in 1804, when it seems nearly 50 % the remaining inhabitants died.