Keeping the Europeans Out
The Monroe Doctorine
The Americans had to keep the Europeans out
So James Monroe formed the Monroe Doctrine in 1823 so they could gain more land. This policy stated that the United States would not interfere with European affairs if they didn't interfere with the United States. It also warned the Europeans not to try to regain the newly independent Latin American nations.
The American's Side
The Americans made this policy so that the other European nations would not take over the new Latin American countries. If they did, this would result in less land and power for the United States, something that no American wanted. Although if the Europeans tried to interfere with the United States, we would retaliate, something that they didn't want.