Why did some Native Americans ally with either side of the war

The British promised the Native Americans that they would control the expansion of settlers into Indian land.

The British made many promises to the Native Americans to convince them that they should provide support to the British government and military in the Revolutionary War. Mostly over-promising the British provide mere trinkets and low money offers to the Indians who were not aware of they way they were being mislead. In saying this; it does not mean the Patriots were treating the Indians any better.