European colonization and interference in the Western Hemisphere was held in check by the:

Good Neighbor policy

Big Stick policy

Watchful Waiting

Monroe Doctrine

Verified Answer :

European colonization and interference in the Western Hemisphere was held in check by the "Monroe Doctrine," since this was issued by the United States in an effort to claim sovereignty over the entire region. 

Answer:

Monroe Doctrine

Explanation:

European colonization and interference in the Western Hemisphere was held in check by the "Monroe Doctrine," since this stated that the US would treat expansion into the west as an act of aggression.