“It is so easy to be an enemy of the United States, but so difficult to be a friend.”
As quoted in a response to Anna Chennault in 1975
Langguth, A.J. Our Vietnam, New York: Simon & Schuster, 2000 page 656.
Нгуен Ван Тхьеу, также Тхиеу — военный деятель и один из президентов Республики Вьетнам .
Как в российских, так и в зарубежных источниках нередко упоминается просто как Тхьеу, что не совсем официально: Тхьеу — не фамилия, а компонент имени. Wikipedia

“It is so easy to be an enemy of the United States, but so difficult to be a friend.”
As quoted in a response to Anna Chennault in 1975
Langguth, A.J. Our Vietnam, New York: Simon & Schuster, 2000 page 656.
“Of course, I would like to go down in history as the man who brought peace.”
"Thieu Asks an Invasion of North If Paris Peace Negotiations Fail" in The New York Times https://www.nytimes.com/1973/01/14/archives/thieu-asks-an-invasion-of-north-if-paris-peace-negotiations-fail.html (14 January 1973)
"Speech in Saigon" in The New York Times https://www.nytimes.com/1972/10/25/archives/speech-in-saigon-ceasefire-obstacles-seen-but-president-expects.html (25 October 1972)
“Don't listen to what the Communists say, but look at what they do.”
Bushy, D. The World Looked Away: Vietnam After the War, Archway Publishing, 2018 page 2.