Vietnam had been at war for 35 years
It was the US that lost their stomach for more war
And properly so in this case! But many extreme rightwing Americans consoled themselves with the warmongers’ lie that we should have continued that war indefinitely, or used nuclear weapons, or that “we” actually “won” the war but were “stabbed in the back” by domestic communists, pacifists, Yippies, traitors, and Democrats … though the anti-war movement was as hostile toward LBJ as toward Nixon — maybe more so.
It was of course the Nixon / Kissinger strategy to withdraw our troops, counting on “Vietnamization” to provide face-saving “cover,” knowing the final result was inevitably a Communist victory. They put pressure on Russia and China to pressure the Vietnamese communists to sign agreements for this very purpose, to bide their time, and the Vietnamese wisely agreed. At that time neither Russia nor China was willing to abandon Vietnam completely.
Of course “Peace with Honor” was impossible given the U.S. mindset, its unwillingness to provide compensation or humanitarian aid or allow post-war trade relations. Of course both sides knew the negotiations were clearly about giving the U.S. time to save face — without U.S. soldiers on the ground it was inevitable the South Vietnamese generals and government would fall.
Moreover, U.S. hostility toward Vietnam after its victory was so great that by 1979 we were encouraging the Chinese to invade Vietnam to “teach them a lesson” and we supported the remnants of the pro-China Khmer Rouge regime as Cambodia’s “official government” for years in the United Nations after the Vietnamese Army had overthrown it. That expensive Vietnamese decision saved perhaps a million innocents from death in the Cambodian “Killing Fields.”
Like I said … No “peace with honor” but just continuing demagogy and stupid partisan “culture war” in the U.S.A. — brought to us by lunatic warmongering fools.
To be sure, all this was part of the cynical excesses of the Cold War in that period, of fear of “Dominoes Falling.” To a certain extent it relied on traditional U.S. anti-communism and (reasonable but hopelessly simple-minded) pro-democracy instincts. In parts of the (tiny) U.S. “hard left” there was plenty of childish thinking too … and ignorant apologizing for “revolutionary” movements that were in fact reactionary, from Mao’s “Cultural Revolution” in China to (at first) Khomeini’s “Islamic Revolution” in Iran.