How did western expansion affect native americans?

In the 19th century took place in America what was called the westward expansion, which consisted of the movement of pioneers into the American west, motivated in part by the Gold Rush. Such expansion changed Native American life in many ways, affecting it dramatically in terms of making American native leaving their homes, changing their lifestyles as well as the buffalos' killing.

Regarding Native American lands, pioneers made millions of these native to re-group in pieces of government lands, called reservations, which were set aside their former domains with the excuse of making such lands more productive. Reservations from where frequently more land was taken, causing, as a result, a deliberate reduction of buffalo herds.  

In addition, during the westward expansion describe before, Native Americans were also forced to accept the pioneers’ culture as their own and blending in it, which represented a forced assimilation.

an expansion is one of two basic business cycle phases; the other is contraction. the transition from expansion to contraction is a peak, and the changeover from contraction to expansion is a trough.