The land was free and perfect for farming, if settlers survived the journey to Oregon the land was all theirs. But not only did the US like it, Britain and Russia also liked it. So the US told people to move there ASAP so it would officially be claimed by America.
I would say simply the geography but they could also see where they founded their civilization. They could learn about how the romans viewed themselves and the outside world.
The theory of a social contract influenced how American colonists believed their position to be in relation to that of Parliament.
In short, that if one is going to be a part of a government, there needs to be a tangible benefit or service provided.
