The Indians have the strange ability to found new settlements in adjacent tiles to each other's and sometimes adjacent to their own settlements.

One downside I experienced to this is that when I razed an undefended Tupi settlement, the Apache in the next square over declared war on me immediately. My relations with the Apaches do not indicate that I declared war on their friends (I had been at war with Tupi already anyway) or that I had stolen land from them, so I'm not sure what caused the immediate response from them.