I have always heard of the great South American empires however, to my understanding, everything above what is today Mexico stayed relatively primitive in comparison.
Why is it that no great empire or even cities appeared in the north?
/u/400-rabbits and /u/Snapshot52 and /u/Pachacamac have answers for you in the thread If ancient humans migrated into the Americas via a land bridge across the Bering Sea...why are the oldest settlements in the Americas located in Central America and South America, with relatively younger and less evidence of ancient peoples in North America? (somewhat paraphrased because it is a long question), the first two represented by links to previous answers.
see below for another link