Imperialism is defined as the policy of extending a nation's authority by territorial acquisition or by the establishment of economic and political hegemony over other nations; manifest destiny is the idea that God gave a nation the right to practice this. With a continued splintering (due to a lack of party-defining issues) of the American political system, the exertion of American ideals upon other nations was one of the few topics that was left for the two major political parties (Whigs and Democrats) to disagree about. The American policy of acquiring certain choice territories can be labeled as nothing but aggressive imperialism; both the term and idea of manifest destiny were a rationalization of said imperialism. America's efforts to acquire Cuba, the acquisition of Texas (along with the Gadsen purchase), and the procurance of Oregon and California, were all exercises in aggressive imperialism, which was euphemized (and rationalized) as manifest destiny.
America's attempt at acquiring Cuba was initially a peaceful proposition to Spain of 100 million dollars. Spain, still grudging America the conquering of Florida and other territories, refused the proposition. The slave holding states in America, attempted to take Cuba by force in order to shift the balance of states in the slavery question. This private militia while not acting for all of America, served as an aggressive force attempting to frighten Spain out of Cuba and establish American hegemony.
The annexation of Texas was a furthering of American western hemispherical dominance. The United States government had no interest in helping the Republic of Texas until the Texans sued for European aid. Fearing possible infringements of the Monroe Doctrine, the United States annexed Texas and began acquiring Mexican territories such as the purchase of the Mesilla Valley. This