Congress has issued no declarations of war since the early 1940s, when it did so against Nazi Germany, Imperial Japan, and other Axis powers. Yet the United States has launched more than a dozen significant "presidential wars" since then. Moreover, that pace shows little sign of slowing.

Most analyses of the rise of the imperial presidency since World War II have focused on the executive's inexorable usurpation of congressional war powers – although a more wide-ranging view. Usurpation indeed has been the dominant factor. When Harry Truman sent more than 200,000 US troops to intervene in the conflict that had erupted on the Korean Peninsula, he showed no inclination whatever to seek a declaration of war from Congress. Indeed, he acted as though getting a resolution from the United Nations Security Council authorizing member states to send forces was more legally relevant than getting any kind of congressional approval. Later presidents likewise ignored Congress and acted entirely on their own alleged authority (Johnson in the Dominican Republic, Reagan in Lebanon and Grenada, Obama in Libya). In one case (Clinton in Kosovo), a president even disregarded the legislative branch's refusal to give approval for military action. More often, though, White House occupants preferred supportive, "blank check" congressional resolutions (Johnson in Vietnam, the elder Bush in the Persian Gulf, and Bush the younger in Afghanistan and Iraq).