Sure, in some instances that was the case, but it's wrong to assume that indigenous north Americans didn't have cities or large scale agriculture.

Agricultural practices in Cahokia for instance, wasn't a European style monocrop. Rather, "Farming at Cahokia was biologically diverse and, as such, less prone to risk than was maize-dominated agriculture" ^(see link above)^

And Cahokia was, for a time, the political and economic center of much of indigenous north American, with the city itself being of comparable size to many European cities in the same period.