The answer is the destruction of the buffalo.
While military victories were significant, they were not the sole or even the primary reason for the white victory over the Native Americans. The battles were part of a larger strategy that included other factors.
The destruction of the buffalo was a critical factor in the white victory over the Native Americans. The buffalo was a central part of the Plains Indians' way of life, providing food, clothing, and materials for shelter. By systematically hunting and nearly exterminating the buffalo, white settlers and the U.S. government effectively undermined the economic and cultural foundation of many Native American tribes, leading to their eventual defeat and displacement.
While some Native Americans did adopt certain aspects of white culture, this was not a major factor in the white victory. In many cases, adoption of white ways was a survival strategy rather than a cause of defeat.
Manifest Destiny was a driving ideology behind the westward expansion of the United States, which justified the displacement of Native Americans. However, it was more of a motivating belief than a direct cause of victory. The destruction of the buffalo had a more immediate and tangible impact on the Native American way of life.