The Gadsden Purchase, named after James Gadsden, the embassador at the time, was an extension piece of U.S. soil. The purchase followed the acquisition of the Mexican Cession. It was the last purchase of the seven major land purchases, and signified the border of the U.S. and Mexico. The main purpose was to serve as a route for an extreme south transcontinental railroad, but it also was an opportunity to get land from the Mexicans. It was a marker for the end of the Treaty of Guadalupe-Hidalgo, the end of the Mexican-American War.

The Ostend Manifesto, issued by the United States in 1854, stated that the U.S. would take over Cuba by force if the spanish wouldn't let them buy it for 120 million U.S. dollars. The outcome was one of outrage from the republicans, they thought that they had an imperialist government on their hands. Suspicion of bolstering the south's interests also was laid on the Democratic party. This was important because it meant that the U.S. was drifting away, temporarily, from their isolationist policies. The Ostend Manifesto was considered a threat across the European nations, because it hinted that the U.S. would start imperialism.