Social democracy has generally been considered one of the most successful political forces of the 1900s. The Nordic model, building on the institutionalized, corporatist collaboration between capital, labour and state and long extolled as a successful compromise between a communist planned economy and free market capitalism, has close links to Nordic social democracy. The organizational home of Nordic social democracy has been the Social Democratic parties; working-class dominated mass parties with deep roots in trade unions and popular movements. In the mid-20th century, to follow the political thread, social democracy formulated an objective that found more mass support than any other leftist idea: to offer citizens protection against the inequalities created by an unregulated market. The broad definition of social democracy is, meanwhile, used in an attempt to single out some central features of a common reformist ideology that Social Democrats tried to translate into political action.