The concepts of “limited war” and “flexible response,” in which the U.S. responded to communist aggression with conventional air-ground forces, military aid. advisors, and other assistance, defined U.S. involvement in Vietnam. This reflected the larger U.S. strategy of containing the spread of communism rather than outright defeating it for fear of global nuclear war. As the war progressed however, North Vietnamese Army (NVA) activity in the South forced the U.S. political leaders into a situation in which they either had to escalate U.S. involvement in the war or abandon South Vietnam to the Communists. President Lyndon Johnson was careful to monitor and manage the escalation, limiting the conflict to the South and abandoning the total war tactics of WWII. He went so far in his micromanagement of the war as to personally select targets for bombing in the North.
The 1968 Tet Offensive had serious repercussions in the U.S. While it resulted in a tactical victory, it convinced many political elites who previously thought that progress was being made, to believe that the war could not be won at a cost acceptable to the American public. The anti-war movement in the U.S. ramped up and by the end of 1968 there were seven million active protesters. While the Soviets supplied the NVA and Viet Cong with arms and supplies, they also channeled millions of dollars into the U.S. anti-war movement through the KGB managed World Peace Counsel and other pro-peace/anti-war organizations. The Soviet Military Intelligence Directorate (GRU) and the KGB together actually had a larger budget for funding the anti-war movement in America and abroad than it did for military and economic support of Vietnam. The Soviets eventually spent more than $1 billion on anti-war propaganda and support for the anti-war movement. It was a hugely successful campaign that eventually resulted in strategic communist victory in Vietnam.
Due to flagging support for the war Johnson began a process of de-escalation that later became known as Vietnamization. After his election in 1968 President Richard Nixon continued the process of Vietnamization in which the U.S. reduced the number of forces in the South and strengthened South Vietnamese forces. The effort also focused on “winning hearts and minds” by providing security, building infrastructure, and funding social programs. What we might call nation building today. Combined with these efforts, Nixon took a hardline “madman” stance designed to make the communists think that he would do “anything” to end the war. Acting the part, Nixon authorized covert and overt incursions into Cambodia and Laos to disrupt the pipeline that fed the communist war effort in the South. He also mined Northern ports and waterways, instituted a naval blockade, and ramped up strategic bombing of the North with Operations LINEBACKER I and LINEBACKER II.
Eventually these last hardline actions brought the North to the negotiating table. They wanted the U.S. out of the war and signed a treaty in which they agreed to the rights of self-determination and national sovereignty for the South Vietnamese. They also promised not to move troops south across the 17th parallel nor to use force to reunify the country. U.S. diplomats knew the North likely had no intention of honoring the document, but they had their “peace with honor.”
General Creighton W. Abrams, of WWII fame, best described the U.S. Vietnamization effort when he called it a “slow surrender.”
 Allan R. Millett, Peter Maslowski, and William B. Feis, For the Common Defense: A Military History of the United States from 1607 to 2012 (New York: Free Press. Kindle Edition, 2012), Kindle Location 9918.
 United States Department of Defense, Secretary of Defense, Top Secret-Sensitive: United States – Vietnam Relations 1945-1967, by Vietnam Task Force, IV. C. 7., vol. II, The Air War in Vietnam, 105-107, accessed June 18, 2018, https://www.archives.gov/research/pentagon-papers.
 Millett, For the Common Defense, Kindle Locations 1804-1808.
 Ion Mihai Pacepa, Disinformation: Former Spy Chief Reveals Secret Strategies for Undermining Freedom, Attacking Religion, and Promoting Terrorism (Washington, DC: WND Books. Kindle Edition, 2013), Kindle Locations 5290-5294.
 Ibid. Kindle Locations 898-904.
 Stanislav Lunev and Ira Winkler, Through the Eyes of the Enemy: The Autobiography of Stanislav Lunev (Washington, DC: Regnery Publishing, 1998), 78-79.
 Millett, For the Common Defense, Kindle Locations 10841-10843.
 Ibid. 10896-10900.
 Ibid. 10947.