Following the war, de Seversky remained in the United States. He became a U.S. citizen in 1927, whereon he was commissioned a major in the Air Corps Specialists Reserve. He became a prominent aircraft designer, developing numerous significant technical improvements and innovations. In 1922, de Seversky formed the Seversky Aero Corporation, reorganized and expanded in 1931 as the Seversky Aircraft Corporation.
From the 1920s until his death, de Seversky was a dedicated advocate of the strategic importance of airpower, working relentlessly to enhance U.S. aviation and eventually its missile and satellite capabilities. Between the wars, he collaborated with Brigadier General William "Billy" Mitchell on tests designed to prove the superiority of airpower over battleships, efforts that de Seversky's close ties to the American military, flair for publicity, and continuing record-breaking flying feats greatly facilitated.
World War II and its aftermath won de Seversky's message a favorable hearing. Besides lobbying politicians and the military, he published numerous newspaper articles and three books on the indispensability of airpower to modern warfare—all urging that the U.S. Air Force become the world's strongest. Victory through Air Power (1942) became a Walt Disney film that both President Franklin D. Roosevelt and Prime Minister Winston L. S. Churchill admired. Air Power: Key to Survival (1950) and America: Too Young to Die! (1961) reiterated the themes. De Seversky died in New York City on 24 August 1974.
de Seversky, Alexander P. Victory through Air Power. New York: Simon and Schuster, 1942.; Griffiths, David R. "De Seversky, Alexander Procofieff." In John A. Garraty and Mark C. Carnes, eds., American National Biography. 24 vols. New York: Oxford University Press, 1999, vol. 6, pp. 480–482.; Leary, William M., ed. Aviation's Golden Age: Portraits from the 1920s and 1930s. Iowa City: University of Iowa Press, 1989.; Warner, Edward. "Douhet, Mitchell, Seversky: Theories of Air Warfare." In Edward Mead Earle, ed., with Gordon Craig and Felix Gilbert, Makers of Modern Strategy: Military Thought from Machiavelli to Hitler. Princeton, NJ: Princeton University Press, 1943, pp. 483–503.