China people talk about kindness, which was a long time ago in the Spring and Autumn Period. During the Warring States period, it was a meaningless war. The battle of Changping killed 400,000 people. Can not be said to be cruel, soft-hearted people are doomed to failure.
Then take the distance between the three countries. Liu Bei borrowed Jingzhou and refused to return it. He was invited by his relative Liu Zhang to help. As a result, his territory was occupied, but if he didn't do so, Liu Bei couldn't earn any territory.
Finally, back to the Indians, they are savage and have serious infighting. Killings between different tribes will be scalped as trophies. In fact, one of their major purposes of being friendly to Americans is to let Americans help them beat their compatriots.
Moreover, when European countries competed for territory in North America, Indians were not idle. Their different tribes formed alliances with the British and the French respectively and fought hard against each other.