It is difficult to pinpoint the moment at which America crossed from Republic into Empire but guidelines exist for doing so. In his treatise Rise of Empire (1952), the libertarian journalist Garet Garrett declared the "first requisite of Empire" to be "the executive power of government shall be dominant." Arguably, the power most intimately connected to Empire or imperialism is conducting foreign policy, especially war.

America's plunge into imperialism is evident in its abandonment of a constitutional clause. Article I, Section 8, Paragraph 11 (the "War Powers Clause") reads, "[The Congress shall have power …] To declare war, grant letters of marque and reprisal, and make rules concerning captures on land and water." The form of the declaration is not specified but the need to go through Congress is.