Final answer:
Manifest Destiny contributed to the decline of Native American populations through intermarriage, conflicts and violence, and the spread of diseases leading to loss of hunting grounds.
Step-by-step explanation:
Manifest Destiny contributed to the decline of Native American populations through intermarriage and cultural assimilation, conflicts and violence, and the spread of diseases leading to the loss of hunting grounds.
The Americanization policy formulated by reformers sought to assimilate Native peoples to a Euro-American model, which led to the destruction of Native cultures.
Additionally, economic policies, such as the depletion of natural resources and violence against Indigenous populations, further contributed to their depopulation.