During the 19th century the American navy was not strong enough to export American power across the Atlantic (Certainly not enough to compete with the European Imperial Powers). It wasn't until the very late 19th century and early 20th century that the US started to build up their Navy and even then their imperial efforts focused first in the western hemisphere with the Spanish-American war in which they acquired Cuba and the Philippines. Then they tried to get into Mexico by backing Pancho Villa only to remove their support later. The Americans didn't really cross the Atlantic untill World War One.