system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why are there no large Native empires in North America the way the Mayan and Aztec were in Central/South America?

From North America - traveled to Central and South America and saw these big beautiful ruins of the past. A bit of research shows that these vast empires existed but were (wiped out by colonizers?) so why are there no big city ruins in North America? \[For example, Xunantunich\]
gpt
South and Central American cultures were essentially based on agriculture and domesticated animals. In other words, they were very stationary cultures that could produce a lot of food relatively reliably.

North American cultures were much more reliant on migratory animals like caribou, buffalo, and seasonal fish like salmon. There were some large native American nations but relatively little permanent settlement.

In addition, South America is essentially a greenhouse producing an abundance of food with many rivers acting as highways for transporting food and other goods. By comparison, much of the North American heartland consists of enormous expanses of desert and field. It's difficult to transport large amounts of goods across these lands, which is why many North American cultures focus on staying mobile.

North America did have some agrarian cultures surrounding the wetter areas but it still lacked good ways of transporting the bounty those people might grow.

So in short, South/Central America encouraged permanent stationary development of their civilizations while North America encouraged migratory cultures that didn't invest heavily in trying to grow large stationary populations.