This seems a pretty loaded question.

...the Americas didn't seem to want to expand, or build empires?

You're grouping a large number of different peoples and states (including some that have been called empires) spanning an entire continent (or two, depending on your POV) across a huge stretch of time.

That being said, the FAQ has quite a few threads on the pre-columbian Americas.

The top comment in this thread might be a good place to start. It's about technology as opposed to expansion, but it's a good look at some of the misconceptions that often surround this topic.