There were many reasons why the USA agreed on a ceasefire with North Vietnam on 28 January 1973 after around a decade of its interference in the Vietnam War. By agreeing a ceasefire, the USA failed to obtain its original objective for entering the War--save South Vietnam from communism, and to prevent the first domino from falling. The causes can be divided into different categories, militarily, economically and socially. In addition, the political factors had certain contribution to this matter as well.
Militarily, the US troops' will of continuing the fighting diminished considerably in the late 60s and early 70s because of the long duration of the war, the determination of the Vietminh, and the fading hope for victorious. Tet Offensive in 1968 was where the North Vietnamese started an attack on most of the major cities in the South; apparently, the US won this offensive because the relatively small casualty it suffered, 1536 killed in action compared to the North's 45,000 .
English: From Captain Moyars S. Shore II, The Batt...
English: From George L. MacGarrigle, The United St...
U.S. Marines move through the ruins of the hamlet ...But in fact, the North won in this offensive because it shaken the will and morale of the US soldiers and the US citizens considerably. An U.S. Marine Lieutenant Philip Caputo once said in a CNN interview about the Vietminh, "Their fighting spirit did impress me. I'll say that the local guerrillas and even some of the main force units were absolutely -- even without air power, without artillery, just one to one, man-to-man so to speak -- were no match for us. We were much better than they were. But when you got up a level there, their fighting spirit and morale and abilities I think were quite impressive" This was the view of a man who had fought the Vietminh, and even he thought that the Vietminh's determination to win this war was quite impressive...