Solidarity
The Polish trade union that grew to ten million members, survived martial law, and won the 1989 elections that began the Eastern bloc's collapse.

In August 1980 an out-of-work electrician named Lech Walesa scaled the fence of the Lenin Shipyard in Gdansk and took charge of a strike. What began as a protest over the firing of a crane operator and the price of meat became the first independent mass movement the Soviet bloc had ever seen. The workers won a written agreement, the Gdansk Accords of August 31, that granted them the right to organize outside Party control. The union they built, Solidarnosc (Solidarity), grew within a year to roughly ten million members, about a third of Poland's working-age adults. No communist regime had ever faced anything like it.
A workers' revolt against a workers' state
The genius and the threat of Solidarity was that it turned communism's own language against it. A state that claimed to rule in the name of the proletariat was now confronted by the actual proletariat, on strike, demanding rights. It was never only a union. It fused shipyard welders with dissident intellectuals and the Catholic Church, whose authority had just been magnified by the 1978 election of a Polish pope, John Paul II, and his electrifying 1979 pilgrimage home. For sixteen months Poland experimented with a freedom no Warsaw Pact country was supposed to have, and Moscow watched with alarm.
Martial law and the long underground
On December 13, 1981, General Wojciech Jaruzelski declared martial law, arguing that he was preempting a Soviet invasion. Tanks took the streets, Solidarity was banned, and roughly ten thousand activists, Walesa among them, were interned. The movement was driven underground but not killed. It survived on smuggled printing presses, church basements, and Western attention, and Walesa collected the 1983 Nobel Peace Prize while effectively under surveillance. The regime had the guns; Solidarity had the legitimacy, and a stagnant economy kept proving the union's point.
The first domino
By 1989 the Polish government was bankrupt of both money and authority, and it did the one thing the system was built to prevent: it negotiated. The Round Table talks in the spring of 1989 legalized Solidarity and scheduled partly free elections. On June 4, Solidarity candidates won all but one of the seats they were allowed to contest, a defeat so total the communists could not form a government. In August, Tadeusz Mazowiecki became the first non-communist prime minister in the bloc. Poland had not been liberated by an army or a foreign power; it had voted its rulers out. Within months East Germany, Czechoslovakia, and the rest followed, and the wall came down.
Walesa completed the arc in December 1990, moving from the shipyard gate to the presidency of a free Poland. The union he founded did not last as a political force; it splintered once the enemy that defined it was gone. But its single achievement is hard to overstate. Ten million ordinary people had shown that the Soviet bloc could be cracked from the inside, by workers, with signatures instead of guns, and that the crack, once opened, would not close.