Social Organization. Individuals usually identify themselves with the named clan and subclan ( sem onda and sem kank, meaning "large family" and "small family," respectively) of their father; while this social identity is defined by birth, it can be renegotiated by continued residence in a place and "brotherly" cooperation in clan events. Clanship is a relationship of shared responsibility: for example, for collective defense, for making contributions to clan-sponsored prestations, and for giving unsolicited aid in small-scale wealth distributions at times of marriage and death. In counterpoint to their clan obligations, over the course of their lives individuals also create networks of exchange (twem) partnerships with affines, maternal kin, and other nonclanmembers, on whom they depend whenever they need valuables (e.g., pigs, pearl shells, money). A person's external exchange partnerships constitute the source of his or her personal "autonomy" and power within the clan. The structures of interclan alliances and individual exchange partnerships only partially correspond with one another. While clanship is predominantly a relation among men, twem partnerships can also be constructed between women and men and among women. Local groups are generally known by both a place and a clan name (e.g., Senkere Molsem). Such local clan sections have close sociopolitical relations both with other sections of the same clan living in different localities (e.g., Molmanda Molsem)—whether or not they are contiguous—and with neighboring sections of different clans belonging to the same tribal alliance. Among members of one tribal alliance of clans, contiguity creates stronger relations of cooperation than does common clanship.
Political Organization. There are no formal councils or inherited positions. Leadership is achieved by consistently exemplary contributions to clan wealth distributions and by an outspoken, active interest in shaping clan policy through private persuasion and public oratory. Political participation in interclan wealth distributions—whether by big-men ( ol koma ) or ordinary men—depends at least as much upon having created a personal exchange partnership network as it does on having a large, productive household and direct access to female labor. Women are excluded from clan policy making. Whereas nonagnatic status may have disadvantaged men (e.g., preventing them from becoming big-men) in the past, it no longer does. While there is no political organization encompassing the Mendi Valley as a whole, territorially contiguous clans often ally themselves as pairs into named tribes of up to about 1,500 members. Neighboring tribes—comprising perhaps 3,000 people—who support one another in warfare and exchange, may refer to one another as "brothers" and link names (e.g., Surup and Suolol becoming Surup-Suol).
Social Control. There are moral restrictions on bloodletting within the clan and, to a lesser extent, between clans. It is thought that ancestral spirits ( temo ) will mete out justice in cases of intraclan violence. A strong moral emphasis on reciprocity—reinforced by fears concerning jealousy-induced sorcery and witchcraft—encourages people to participate in the exchange of wealth.
Conflict. Prior to colonial rule, Mendi tribes and clans were the main war-and peace-making units. After 1950, local warfare was suppressed as a main means by which the Australian administration established its authority. However while bow-and-arrow warfare did decline, conflict continues to this day under the rubric of sorcery ( tom ). That is, Mendi consider most deaths (except those among infants and the aged) to be politically motivated; they insist that collectivities accept responsibility for death by making public wealth compensation ( maike ) to the group of the deceased.