The War Powers Resolution (1973), which restricted the president's emerging powers to make war, was an effort by Congress to protect and reaffirm its constitutional prerogatives in foreign affairs. The constitutional delegation of powers in foreign policy, particularly in relation to warmaking authority, is fairly straightforward. Congress declares war, and the president "makes" or conducts it in his capacity as Commander in Chief. Relying on the "implied" or "inherent" executive authority to respond quickly and decisively to enemy attacks, however, during the twentieth century presidents sent American troops into conflicts of ever-increasing scope without prior Congressional declarations of war. President Theodore Roosevelt's "Roosevelt Corollary" to the Monroe Doctrine, for instance, provided for American intervention into Western Hemisphere countries, and such interventions were often of a military nature.

The real change in war-making authority occurred with the United States's emergence as a major world power after...