Russia, not a regional power here, + Cuba = revolutionary intrusion in neighboring countries for 40+ years = raw nerve.
The Monroe Doctrine was a US foreign policy regarding Latin American countries in the early 19th century. It stated that further efforts by European nations to colonize land or interfere with states in North or South America would be viewed as acts of aggression, requiring U.S. intervention. At the same time, the doctrine noted that the United States would neither interfere with existing European colonies nor meddle in the internal concerns of European countries.
Our activities in Europe are directly related to 1) most of us having backgrounds there and 2) Europe's regular seppuku attempts and habit of setting up the next war by retributions for the last one. Many of us are unconvinced it won't happen again without structures like NATO etc.