Mixed nations and borders. You can use the question itself to get the answer, since imperialism left such a strong legacy in africa, the borders were so defined and the natives were forced to abide by them. So there is no reason for there to be any confusion about what is where.
I’m pretty sure they fought and conquered neighboring tribes. They also had Tenochtitlan, the capital, in the middle of lake Texcoco, which provided protection. They then defeated more tribes and taxed the tribes until the Aztecs were flourishing where they were invaded by Hernan Cortez
