Under james monroe, the united states expanded by:

strenghtened american foreign policy in 1823

Explanation

The MONROE doctrine, a warning to european countries  against further colonization and intervention in the western hemisphere

answer: ensure protection from communism

explanation:

the north atlantic treaty was largely dormant until the korean war initiated the establishment of nato to implement it, by means of an integrated military structure: this included the formation of supreme headquarters allied powers europe in 1951, which adopted the western union's military structures and plans.

the anwser is missions