The Framers of the U.S. Constitution assigned to Congress many of the powers of external affairs previously vested in the English king. That allocation of authority is central to America’s democratic and constitutional system. When decisions about armed conflict, whether overt or covert, slip from the elected members of Congress, the principles of self-government and popular sovereignty are undermined. Political power shifts to an executive branch with two elected officials and a long history of costly, poorly conceived military commitments. The Framers anticipated and warned against the hazards of Executive wars. In a republican form of government, the sovereign power rests with the citizens and the individuals they elect to public office. Congress alone was given the constitutional authority to initiate war.
Legislative control over external affairs took centuries to develop. The English Parliament gained the power of the purse in the 1660s to restrain the king, but the power to initiate war remained a monarchical prerogative. In his Second Treatise on Civil Government (1690), John Locke identified three functions of government: legislative, executive, and “federative.” The last embraced “the power of war and peace, leagues and alliances, and all the transactions with all persons and communities without the commonwealth.” To Locke, the federative power (what today we call foreign policy) was “always almost united” with the Executive. Any effort to separate the executive and federative powers, he counseled, would invite “disorder and ruin.”