Keep in mind that the Cahokia city was contemporay with the large cities in Arizona, the Chaco culture and the Phoenix basin.
The peoples of the east, knew and traded with the west. The Southwest cities traded with the cities to the south. Thus, there was wide spread commerce that crosses the artificial present border with Mexico.
The key fact un mentioned is the source of the copper. Did it come from Tennessee or from Arizona?
Aside, I use the same technique of forging and annealing in my studio today. I have a little rolling mill that eases the hammering task and a gas torch for annealing and don’t use stones.
Also, before bending, a line, even a curved line can be scored with perhaps a flint to assure the break along a desired line
“The Southwest cities traded with the cities to the south. Thus, there was wide spread commerce that crosses the artificial present border with Mexico.”
Well, I have read that linguists find links in some southwest tribal languages to very ancient precursors to both their languages and some languages south of the Rio Grande - suggesting very ancient migration from north to south.
But, in terms of contemporaries of the peoples around Mexico City such as the Mexticas and the later Aztecs, their social and “civilizing” sphere of influence is documented to NOT have extended much more than a couple hundred miles north of Mexico City. Suggesting some trade with north of the Rio Grande? Yes. Wide spread? No.
So please site some evidence of the “wide spread commerce” you speak of.
“The key fact un mentioned is the source of the copper. Did it come from Tennessee or from Arizona?”
The likely source for the copper used at Cahokia (southern Illinois) is the ancient large copper deposits in Michigan. The “highways” for that trade would have been the great river systems of the Midwest - the Mississippi, Missouri, Illinois, Ohio and Tennessee rivers.