Dominant Parties

Parties are considered dominant if they achieve electoral dominance both vertically and horizontally. Vertical electoral dominance is achieved when a party surpasses a threshold of vote or seat shares. In the literature, the demarcation of this threshold varies from a majority of at least 40% to 70% of raw votes or lower-house seats. Horizontal electoral dominance requires such a majority to be sustained longitudinally—usually over a generation. For example, Italy's Christian Democratic Party, an archetypal dominant party, controlled the parliamentary executive for 36 years (1945–1981).

Dominant parties often amount to an infraction on the “alternation rule” that requires meaningful democracies to have regular and intermittent exchanges of power between major political parties. As such, dominant parties emerge frequently in so-called partial democracies where electoral competition is ostensibly open but less than fair. A number of obvious explanations account for the rise and persistence of dominant parties in illiberal democracies: electoral fraud, corruption, oligopoly, control by the dominant party of public finances and its usurpation of the national mythology, or a submissive attitude to authority among citizens. In advanced democracies, however, the emergence of dominant parties is perplexing. By definition, a healthy democracy should contain a vigorous culture of opposition politics. Moreover, the dominant party phenomenon hardly squares with studies in organizational behavior that illustrate how these kinds of bodies should be particularly arthritic in adapting to change over time. Hence, a robust understanding of the emergence, persistence, and breakdown of dominant party systems depends on advances in the theory of political competition. Attempts to explain dominant-party systems have focused on either the demand side of the problem by studying electoral behavior, the

supply side of the problem by examining party behavior, or by investigating the role of structure.

Some approaches from electoral behavior argue that dominant parties are sustained either by a lack of social cleavages that would stimulate greater political competition or by the absence of voter dealignment from the dominant party. These approaches have found limited empirical corroboration. In cross-polity analysis, the number of political parties does not seem to correlate with social cleavages when political competition is measured against ethno-linguistic fractionalization. Meanwhile, dealignment explains little when one observes how negative retrospective voting often fails to translate into positive prospective voting for the opposition. Structural approaches have argued that the number of major competitors in a party system is shaped by institutional factors such as district magnitude or the choice of electoral formula. However, the explanatory power of this argument is weak because the collection of electoral systems within the population of dominant party systems is heterogeneous. [Page 203]Supply-side models have attempted to explain the number of competitors in a party system by calculating when it is rational for parties to be formed. Although such models have demonstrated high internal validity, they tend to assume a neutral political market, where parties enter with the same relative advantage and voter preferences are accurately distributed across a left-right spectrum. Other approaches have attempted to advance theories of party behavior via a more realistic account of the asymmetries in resources between opposition and incumbent parties. Single-party dominance may also be attributed to the shortcomings of opposition performance. Some suggest that dominant-party systems place centrifugal ideological pressure on opposition parties, framing them as antiestablishment, niche parties that subsequently fail to attract the support of the median voter.

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