Gdańsk is Poland's principal seaport located in the Kashubian region on the Baltic Sea. Together with the spa town of Sopot and the industrial city of Gdynia, it forms a conurbation known as Trójmiasto ("Tricity"). It has a complex political history with long spells of Polish rule interspersed with periods of German control and two spells as a free city. As an important port and shipbuilding center, the picturesque city was a member of the Hanseatic League. For much of its history the majority of its inhabitants were German speakers who referred to their city as Danzig, but after World War II it became firmly Polish. Gdańsk is the birthplace of the Solidarity movement which, led by Lech Wałęsa, played a role in bringing down the communist rule across Central Europe.