A small clarification: pre-Columbian Mesoamerica did have copper and bronze metalworking, after picking it up from contact with South American societies some time between 600 and 800 CE. The Nahuas (Aztecs) had bronze axes called tlaximaltepoztli, for example. Macuahuitls might have just been better at cutting than bronze blades, though. Societies that learned about ironworking mostly replaced their bronze weapons with it, after all
Ahh, good points all round