A coalition is a combination of political parties or groups to run a country's government, or an alliance of nations in international relations.
In a parliamentary system, coalitions are formed when no party receives a majority in an election. The party with the largest plurality generally takes the lead in forming a coalition majority with other minor parties.
Coalition governments are usually found in countries where many political parties exist, and a single party rarely wins the majority.
The UK has had several coalition governments, including throughout World War I and World War II. As of 2018, the UK is presently under a coalition government, Sweden has spent months trying to form a new coalition government, and the German coalition which has ruled for two decades is crumbling.
The two major parties consist of coalition groups. Presently the Tea Party is a coalition group in the Republican party, and the Democratic Socialists are a coalition group in the Democratic party. Labor Unions, RINOs, environmentalists, pro-life groups, liberals, conservatives, establishment types and many other subdivisions are also coalition members in both parties.
The Democratic party has a history of melding coalition groups with divergent agendas together under the Marxist banner of class struggle. For example, the melding of the Feminist movement in the 1970s and Gay rights movement in the 1990s with the African American civil rights movement. Typically in these grand coalitions, one group gets elbowed aside and becomes the loser.
Some groups' agendas are in direct conflict with each other -- for example the moral issue of civil rights based on condition of birth verses homosexual rights based on a choice of lifestyle. In the coalition of environmentalists and labor unions labor unions turned out to be the big losers as workers jobs were shipped overseas in the name globalism and climate change. While environmentalists supported efforts like clean air and alternative fuels, automobile makers jobs were destroyed by increasing regulations. Such policies led to cutbacks and layoffs.
The term "coalition" also may refer to an alliance of several nations against other countries. Often, such coalitions are formed directly before or during the course of a war. The coalitions formed before World War I greatly magnified an event that should have been handled internally and quietly. Coalitions were also formed during the reign of Louis XIV and during the Napoleonic wars.