What were some of the negative effects of manifest destiny?

The brunt of the negative effects were experienced by the Native Americans.

Explanation:

The idea that it was the destiny of Americans to expand westwards made them disregard the centuries old territorial and cultural boundaries of the aboriginal people. This expansion wiped out complete tribes, caused new tensions, and many wars. It made the expansionist greedy and entitled which continued to fuel the hunger for expansion. This also created tensions with bordering Mexico. This also caused an increase in slavery as more arable land was rapidly acquired and manual labour greatly increased in demand.