Final answer:
The Miami Indians fought against the Americans because the American settlers took their land.
Step-by-step explanation:
The Miami Indians fought against the Americans primarily because the American settlers took their land. As more Americans pushed westward, they came into conflict with Native tribes that had long been living on the land. The Miami Confederacy, a group formed by various tribes of the Ohio Valley, declared the Ohio River as the boundary between Indian and American lands and refused to honor treaties signed by only one individual or one group, which they referred to as 'partial treaties.'