Final answer:
The spread of white settlement in the late 1800s led to the destruction of bison herds in the Great Plains, as settlers disrupted migration patterns and the government pushed Native American tribes onto reservations.
Step-by-step explanation:
The main impact of the spread of white settlement throughout the Great Plains and West during the late 1800s on the regional environment was a steep decline in the existing bison (buffalo) population through hunting. As settlers moved in, they transformed the landscape by building railroads, farms, and ranches. This encroachment severely disrupted buffalo migration patterns and consequently decimated their numbers. Plains groups, which included various tribes like the Crow, Comanche, Arapaho, and Sioux, had traditionally engaged in some agriculture but became more nomadic hunters and gatherers due to the reintroduction of the horse by the Europeans. Additionally, efforts by the government to confine Plains Indians to reservations further eroded their traditional ways of life. The arrival of settlers advanced Manifest Destiny but also expedited the destruction of bison herds, a resource critical to the native tribes' economies.