What allowed native americans in mexico to settle cities larger than those in areas to the north?

One of the main factors that allowed Native Americans in Mexico to settle cities larger than those in areas to the north was that Central America contained far more gold and riches that acted as currency and boosted the economy. Practically no gold was found in what is now the eastern United States. 

Militarism is the answer.

The muslims ruler the mandated and cultural toleration was osman