From 1949 to 1990, the main political parties were the Social Democratic Party of Germany (SPD) and the Christian Democratic Union (CDU), with its "sister party", the Christian Social Union of Bavaria (CSU). After the reunification of Germany the Green Party and Alliance '90(Bündnis 90/Die Grünen) became more important and was in government between 1999 and 2005. Other important political parties after reunification have been the PDS (Party of Democratic Socialism) which was based on East Germany's Socialist Unity Party of Germany. It joined with The Left Party (Die Linkspartei) of western Germany. In 2007 Die Linke and WASG joined together under the leadership of Oskar Lafontaine