Was détente a failure because it collapsed?

The short answer

• The split that made the triangle possible. The alliance’s collapse had several causes. Khrushchev’s de-Stalinization undermined Mao’s cult indirectly, the Soviet withdrawal of nuclear assistance in 1959 damaged cooperation, and Beijing called Moscow’s retreat in Cuba “capitulationism.” The deeper contest concerned leadership of world revolution. Fighting on the Ussuri in 1969 showed that the dispute had become a military danger. Kissinger’s pricing of the division meant making relations with Washington valuable to each side: neither would want the other to gain the better American relationship.
• Parity made arms control rational. After the Soviet buildup produced strategic parity, neither superpower could safely assume it could strike without suffering retaliation. SALT I limited launcher numbers, and the ABM Treaty restricted defenses, preserving that vulnerability. Defenders regarded it as a stable equilibrium; critics saw a system built on the threat of mutual destruction as madness. The agreements did not cover every weapon. MIRVs allowed more warheads on missiles, and theater weapons remained outside these limits; the Euromissile crisis of Chapter 10 would grow from that competition. Arms control could manage part of the race without ending it.
• Economics pressed both ways. Diplomacy also answered economic needs. Soviet harvest failures beginning in 1972 increased the USSR’s need for Western grain and technology. The United States faced heavy defense costs and a strained monetary system; in 1971 Nixon closed the gold window, ending the dollar’s convertibility under Bretton Woods. West Germany had reasons of its own to seek accommodation: Eastern markets and the reunion of divided families. These different pressures helped make practical agreements attractive.

What it changed

Helsinki’s slow fuse. Helsinki’s rights provisions gave dissidents a standard their governments had publicly accepted. The Moscow Helsinki Group formed in 1976, with Charter 77 in Prague and Poland’s KOR following. Their compliance monitoring brought violations to international attention even as authorities persecuted them. Basket III thus supplied a language for later reformers and for challenges to the legitimacy of Eastern European governments. The effects of an apparently “symbolic” agreement emerged over time.

Détente’s decay: the periphery eats the center. The powers had no agreed code for the Third World. Soviet and Cuban support in Angola in 1975 and the Horn of Africa in 1977–78 persuaded American critics that Moscow was using détente to advance. Moscow could respond that those contests lay outside the agreement and point to Egypt’s movement toward Washington as Western competition. Each side regarded its own involvement as legitimate and the other’s as threatening. The resulting distrust weakened the relationship, and the Soviet invasion of Afghanistan in December 1979 finished the détente phase.

The dissenters institutionalize. While negotiations continued, critics prepared the case for renewed confrontation. Team B and the Committee on the Present Danger argued that détente had ratified Soviet gains and concealed a buildup; Reagan would later campaign on such criticisms. In Moscow, the military-industrial complex continued building, and SS-20 deployment began in 1977. The people, weapons and arguments of the Second Cold War were taking shape during détente itself.