2 methods used by the us to acquire territory

2 methods that the U.S. used to acquire territory would be:
-diplomatic negotiations. for example the U.S. telling the Panamanian leader that the U.S. would help them get their independence from Columbia, if Panama in turn, built the U.S. a canal.
-another method would be strategic warfare. for example when the U.S. gained the southwest area through their victory in the Mexican American war