The first westward surge of settlement reached the:

pacific ocean
rocky mountains
mississippi river
appalachian mountains

The Appalachian Mountains

The American expansion took place between the early 17th century and ended with the admission of the last mainland territories as states in 1912. Most of it consisted on the acquisition of Indigenous lands in what is now the Midwest, Texas, the Great Plains, the Rocky Mountains, the Southwest and the West Coast. This expansion was particularly encouraged through the idea of "Manifest Destiny."

no one really purchased it themselves, it was all america, they had debates etc.

there are many answers to this question, such as a diplomat, ambassador, soldier, united nations employee, cia, etc.