What land deal completed the borders of the contiguous United States?

The Gadsden Purchase

Explanation: The Gadsden Purchase completed the outer border of the United States. (I am not sure if it is asking about outer border or inner borders too, such as states)

lee and grant, both of whom held the highest rank in their respective armies, had known each other slightly during the mexican-american war (1846-48) and began their dialogue by exchanging awkward personal inquiries. characteristically, grant had arrived in his mud-splattered field uniform while lee had turned out in full dress attire, complete with sash and sword.

explanation:

the monroe doctrine is the best known u.s. policy toward the western hemisphere. buried in a routine annual message delivered to congress by president james monroe in december 1823, the doctrine warns european nations that the united states would not tolerate further colonization or puppet monarchs.