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 recieves 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 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.