Why do you think the united dates was so interested in moving westward in the early 1800's

There were many reasons for Westward Expansion:

Lots of easily obtainable land

Lots of mining opportunities, which could result in a lot of money

The fantasy of "adventure"

Leaving the constraints of European life, like low paying jobs

Expanding railroad made it easier to get supplies

And, well ... the west was wonderful back then, everyone wanted a taste of it.