Why did the way of life of many indigenous people in the plains of north america end in the late 1870's?

a politically correct answer.

northernmost part (disputed, administered) - near indira col, siachen glacier - 35.674520°n 76.845245°e

northernmost part (disputed, claimed) - dafdar near beyik pass - 37°24′00″n 75°24′00″e

northernmost part (undisputed) - near dharwas, chambal district - 33.24902°n 76.82704°e

southernmost part (mainland) - cape comorin - 8.06890°n 77.55230°e

southernmost part - indira point in the nicobar islands - 6.74678°n 93.84260°e

distance between:  

1 & 4 - 3070 km

1 & 5 - 3654 km

2 & 4 - 3269 km

2 & 5 - 3885 km

3 & 4 - 2801 km

3 & 5 - 3430 km

explanation:

answer is 1935

because gandhi led a march the sea in 1930 and 5 years later he did it again