From historian of Scandinavia Mary Hilson’s The Nordic Model: Scandinavia since 1945:
Why have the Scandinavian social democratic parties been so successful, at least in Norway, Denmark and Sweden? The question has been pursued with particular interest in Sweden, give the status of the SAP as perhaps the most successful political party, measured by any criteria in the western democracies. For some scholars the main explanation has been sociological. The Scandinavian working classes were unusually homogeneous, lacking significant ethnic or religious cleavages, and they were also highly organized. In 1980, 78 percent of Swedish wage earners were unionized; the corresponding figures for other Scandinavian countries were Finland 70 percent, Denmark 76 percent and Norway 56 percent, which as considerably higher than most other western countries. The Scandinavian social democratic parties seem to have been conspicuously successful in mobilizing their ‘natural’ constituency within the working class. Indeed, until the 1970s Scandinavian politics was notable for the consistency of class-based voting patterns and the lack of supposed ‘anomalies,’ such as the strong working-class support for the British Conservative Party, for example.
Nonetheless, no social democratic party could base its success on the support of the working class alone. Many scholars, therefore, have pointed to the social democrats’ ability to mobilize supporters from other social classes, and to create a broad social consensus in support of their policies. According to Gøsta Esping-Andersen, Scandinavian social democracy ‘distinguished itself by the decision to subordinate class purity to the logic of majority politics. The organization moved from “working-class party” to “people’s party,” its platform addressed the “national interest” rather than the proletarian cause”.’ Of the Scandinavian parties, the SAP was perhaps the most successful in broadening the class base of its support and creating ‘a broad wage-earner coalition of blue- and white-collar workers’. There were several reasons for this success. The first was the high level of unionization among white-collar workers and the SAP’s success in institutionalizing its own power base among this group by introducing economic policies designed to benefit all wage earners. The second was the ‘popular’ (folklig) character of the Scandinavian labour movements, which had developed as part of the nineteenth-century popular movements, most importantly the free church and the temperance movements. Particular characteristics of these movements included their inclusive and democratic organizations, and their emphasis on awakening, education and self-improvement. During the late nineteenth century the labour movement made common cause with temperance societies and other popular movements to campaign for democratic rights, with the result that Scandinavian social democracy developed an ideology that owed as much to the inclusive and democratic idea of the folk or people as to a Marxist analysis of class conflict. This allowed even the most unequivocally radical and Marxist of the Scandinavian social democratic parties, the Norwegian Labour Party, to broaden its electoral appeal to include peasant farmers, fisherman and small traders — the little people or småfolket — during the interwar period.
Indeed, it is the ability to make ideological compromises and form electoral coalitions with other political parties that might be seen as the defining feature of social democratic success in Scandinavia. This was partly driven by the existence of an electoral system based on proportional representation, but it is not the whole story. The success of the Scandinavian social democracy parties was partly the result of their ability to ‘institutionalise mechanisms for collaboration between social groups’ through a corporatist approach to policy making, an arrangement that allowed social democratic governments to govern effectively even where they lacked a parliamentary majority, as in Denmark, for example. In practice, this was achieved through the use of state commissions of inquiry to thrash out the details of new policies before they were presented to parliament, and by negotiations between the representatives of the major interest groups: the trade union federations, the employers’ federations and the farmers. In Sweden the term ‘Harpsund democracy’ was coined to describe the practice of agreeing important matters of policy through informal negotiations between leaders of the trade unions, the employers and the government, which took place at the prime minister’s official country residence at Harpsund. These meetings were hailed as an example of the new spirit of cooperation between labour and capital that prevailed at the time, though they were also criticized or excluding the opposition parties.