In school they taught that the climate in Mexico led to large sugar plantations while the climate of the US led to smaller farms especially in the north. Then this led to a more egalitarian distribution of wealth in the northern US which created the middle class demand that allowed manufacturing to take off. In Mexico the poor were too poor to buy a lot of these manufactured goods while the rich plantation owners could afford superior goods.

I'm not sure how an intelligence based explanation would explain this better.