The term coalition encompasses a wide range of political activities and outcomes. At the most basic level, a coalition is said to exist when two or more political groups or actors agree to pursue some common objective(s), pool resources in pursuit of such common objective(s), and actively communicate during joint action to achieve such common objective(s). In contrast to the competitive, majoritarian, "winner-take-all" approach to politics, coalitions emphasize collaboration and group coordination. Understanding coalitions helps scholars and practitioners answer one of the immutable questions of politics: Why do avowed adversaries sometimes cooperate? If politics is largely about bargaining and compromise, then the transformation of political competitors into allies is of the utmost importance, whatever the situation, setting, or scope.
Researchers and theorists ask three classes of questions about coalitions: those concerning coalition formation, those concerning coalition maintenance, and those concerning coalition termination. Observers of coalition formation attempt to explain, and purport to predict, the outcomes and payoffs to political actors engaged in bargaining over the composition of a coalition. Much less studied but no less important is coalition maintenance— the concerns of coalition maintenance shift analysis from outcomes to processes, asking questions about communication among partners, joint decision making, policy output, and the efficacy of an alliance. A more recent scholarly concern with coalition termination seeks to identify the sources and consequences of coalition breakup.
As a basic unit of analysis in political science, coalitions are scrutinized as they occur among such actors as interest groups in society, political parties in the electorate, legislative factions in representative assemblies, and states in the international arena. There are, for example, constellations of small grassroots groups that coalesce as social coalitions to advance a shared agenda (as illustrated by the Rainbow/PUSH Coalition for advancing civil rights in the United States). There are electoral coalitions in which cooperating political parties agree to transfer voter support to one another in districts where doing so enhances the likelihood of victory (as in France’s double-ballot system for parliamentary elections). There are ad hoc legislative or voting coalitions in which members of political parties agree to join forces in support of specific policy or legislation (as in the U.S. Congress).
Perhaps most prominent in the political science literature on coalitions is the scrutiny given to power sharing or governing coalitions, in which political parties agree to collaborate in the joint distribution of cabinet posts and government ministries. Often, small minority parties located strategically in between major party blocs become "kingmakers," holding disproportionate power to make or break a winning coalition. Outside the Anglo-American democracies, from Italy to Israel and Belgium to Germany, such governing coalitions are typically the norm in parliamentary systems. In international politics, strategic alliances linking two or more states in pursuit of some commonly shared objective may be referred to as coalitions (as in the case of the United States’ "coalition of the willing" designed to oust Saddam Hussein’s regime in Iraq). A rich body of literature seeking to develop and test coalition theories has focused on the motivations that lead political actors to pursue coalitions of different sizes (minimum-winning coalitions or oversized coalitions), ideological complexions, and novelty.
