Answer:
Economic: Acquiring more land would've given more opportunity to current and future settlers. Reaching coast to coast would be better for trade, as well as getting people to settle in these areas with like the homestead act (easy to settle near sources of water and fertile land, rather than midwest)
Social: Manifest destiny is seen as a god given right to america at this point, each president that pushes it, believed and persuaded people into believing this. Reaching coast to coast is also a goal(Similar to like the moon landing) in its impact.
You can say that it is caused by the annexation of texas, mainly due to support for annexation began to form at this point. As well as their land disputes with britain, causing a rise in patriotism and the newly co'ined term 'manifest destiny'
Explanation:
