Solidarity was an independent Polish Trade Union that was founded on the 17th of September 1980, under the leadership of Lech Walęsa at the Lenin Shipyard in Gdańsk.

Solidarity was the first trade union to operate in a Warsaw Pact country that was not controlled by a communist party. Through its first year membership reached 9.5 million members. Membership peaked at 10 million members (about 1/3 of the working population) by its first congress in 1981.

Through the 1980’s Solidarity was a social movement that used civil resistance to advance workers rights and social change. The Polish government attempted to bust the union by imposing martial law and years of political repression.

Throughout these years Solidarity was supported by the Pope and the United States. The financial support provided by the US is estimated to be as much as $50 million.

Despite the best efforts of the Polish government, Solidarity would not be defeated and it was forced to negotiate with Walęsa and his union.

By the end of August 1989 Solidarity formed a coalition government. This was followed in 1990 by Lech Walęsa becoming president of Poland.

Sources:
https://en.wikipedia.org/wiki/Solidarity_(Polish_trade_union)