The purpose of this paper is to examine the dynamism of U.S. psychological warfare from World War II to the Vietnam War by analyzing the experience of a U.S. officer. His name was Monta L. Osborne, and he engaged in psychological operations in China, Japan, South Korea, Okinawa, and South Vietnam from the mid-1940s to early 1970s. This paper focuses on the following three aspects: First, what were the operations that Osborne conducted as psychological warfare against Japanese soldiers and internees during WWII in the China theater? Second, what did he do in Japan during the allied occupation as an expert of secondary education programs and in South Korea during the Korean War as the director of the POW orientation program? Third, how did he conduct public information activities in Okinawa during the U.S. occupation and what psychological operations did he lead against North Vietnam soldiers, officials, and civilians during the Vietnam War? In conclusion, this paper clarified the following three points. First, Osborne’s experiences of psychological operations in China, including the political education/orientation program for Japanese internees, provided helpful keys to developing the GHQ/SCAP education program to diminish ultra-nationalism in Japanese minds and enable them to understand democracy. It pointed out the political complexities that existed between psychological warfare as brainwashing and “democratic education.” Second, his experiences in both China and Japan created an important basis of techniques for two elements of the Korean War: propaganda operations against the North Korean and Chinese people and the POW orientation program of the United Nations Command. Third, Osborne’s experiences in Asia indicated that U.S. psychological warfare techniques were developed as a measure to prevent Communism and infuse democracy into the people not only in enemy countries but also in friendly nations during the Cold War. This paper provides significant keys for considering the historical structure of Asia during the Cold War by studying the dynamism of U.S. psychological warfare from the perspective of Trans-War History.