What was the key to american security during the nineteenth century?

America’s foreign policy has changed over time reflecting the change in its national interest. As a new nation after the Revolutionary War, America’s prime national interest was to maintain its independence from more powerful European countries. Protected by the Atlantic Ocean, its major foreign policy, as typified by the Monroe Doctrine, was to limit European attempts of further colonization of the Western Hemisphere. 

What is the question

Ihave no idea, but i know someone who can you, and it is god. god is always the answer