Nationalism is an idea or movement that holds that the nation should be congruent with the state. As a movement, it presupposes the existence and tends to promote the interests of a particular nation, especially with the aim of gaining and maintaining its sovereignty (self-governance) over its perceived homeland to create a nation-state. It holds that each nation should govern itself, free from outside interference (self-determination), that a nation is a natural and ideal basis for a polity, and that the nation is the only rightful source of political power. It further aims to build and maintain a single national identity, based on a combination of shared social characteristics such as culture, ethnicity, geographic location, language, politics, religion, traditions and belief in a shared singular history, and to promote national unity or solidarity. There are various definitions of a "nation", which leads to different types of nationalism. The two main divergent forms are ethnic nationalism and civic nationalism.