Thereafter, in minor foreign confrontations, presidents frequently employed military force on their own. Historians usually portray William McKinley as resisting jingoes and a yellow press who wanted war with a Spain that posed no threat to the United States. Yet he used humanitarian concern over Spanish abuses in Cuba as a pretext for asking congress to allow him to initiate hostilities. A senator asked, why it should "give the President power to intervene and make war, if he sees fit, without declaring war at all?" Regardless, congress gave McKinley what he asked.

After defeating Spain, McKinley imposed a colonial regime on the Philippines and fought an undeclared war against Filipinos who merely wanted to govern themselves. American troops committed atrocities comparable to those attributed to Spanish colonizers. Theodore Roosevelt continued the war and even defended the American brutalities. He also came up with an exaggerated conception of an inherent presidential war power limited only by specific legal restraints dubbed the stewardship theory.

Woodrow Wilson claimed a similar power, as in his military intervention in Mexico in 1914. He asserted an implied constitutional authority to act as he wished "without recourse to the Congress." In seeking war against Germany, he did not ask congress to declare it but to recognize it had been thrust on the United States. Most historians acknowledge Wilson resorted to military force more often than any previous president but vary in their assessments of the rightness or wrongness of his interventions. They tend also to agree he added to the precedents for the president's unilateral exercise of military force.