Why did Truman call the Korean War a police action instead of asking Congress to declare war?

President Harry S. Truman referred to the Korean War as a "police action" rather than seeking a formal declaration of war from Congress because the U.S. military intervention was conducted under the authority of a United Nations Security Council resolution.12

By acting in accordance with a collective security mandate from the UN to resist North Korean aggression, the administration framed the conflict as an international effort to uphold global peace and security rather than a traditional war between sovereign nations. Because the United Nations itself lacks the power to declare war, the U.S. involvement was tied to the UN's call for member states to provide necessary assistance to restore peace.3412

While this approach allowed Truman to respond quickly to the invasion, it was not without controversy; he faced criticism from political opponents, such as Senator Robert A. Taft, who argued that the president’s unilateral decision to commit troops without congressional approval was a usurpation of constitutional authority.53