[Reily]

Lack of ready tin resources would have been a problem.
I think lack of draft animals was a huge detriment to advancement.

[marktwain]

The Incas new how to cast bronze. They had tin from Bolivia.

The Aztecs had some tin from Zacatecas, and early bronze artifacts have been in the Huastec area of Eastern Mesoamerica.

The American civilizations were just starting to learn to use metallurgy.