Tribes are groups of families bound together by a common ancestor. Smaller groups called clans share ancestors in their immediate family lineage, usually three to five generations back. A group of related clans constitutes a tribe. In patrilineal clans, a person's membership is determined by his father. In matrilineal clans, membership follows the mother's line. The modern nation includes members that share no familial relation. Citizenship, rather than familial continuity, determines membership in a nation.
Nations have land and distinct borders. The borders are usually recognized by other nations and international bodies such as the United Nations. A nation's borders can change as a result of war, annexation or expansion. Tribes' attachment to land varies. Historically, some tribes have had a deep land attachment and have expended great energy securing their borders, just as nations do. Others have a history of movement in which members frequently migrated. Rights to land have been a central theme in the history of both national and tribal warfare and conflict.
From extremely hierarchical rule to consensus-based decision-making structures, the governing methods of both nations and tribes are diverse. Some tribal groups elect representatives to a council, akin to a legislature or parliament. In both tribes and nations, there are varying levels of governance. For example, each clan within a tribe may have its own form of government, just as national government may operate at the federal, state and local level.
The words "nation" and "tribe" are politically contentious and have various meanings for different people. Some people find the term "tribe" offensive, believing that it suggests a less evolved social organization than a nation. Others identify with the term "tribe" as a symbol of solidarity with socially marginalized groups or with their ethnic history. Due to the politically charged nature of these terms, their definitions and common usage are in a constant state of change.