From 1945 to 1975 Thien was an active participant or a personal witness to almost all of the major historic events in Vietnam: the 1945 August Revolution, the 1954 Geneva Conference, division of the country and birth of the Republic of Vietnam, the 1963 coup d'état against Ngô Đình Diệm, the 1968 Tet Offensive in Huế and the April 1975 Fall of Saigon.