Question

Besides land what did the US gain from expansion

Answer 1

It gained more Natural good's and It helped with trade with new Native American's that were already there, and any left resources that the other european powers left.

Answer 2

Besides land, United States gained the various type of natural resources such as Gold, Oil, Coal, and Timber.
The existence of this resources attracted a lot of settlers to come to these newly expanded territories, which will lead to the period of massive economic growth for United States.