Morgan’s discussion of “Growth of the Idea of Government” comprises 60 percent of Ancient Society. By “government,” Morgan referred to what modern anthropologists call social organization and political organization.
Morgan explicitly distinguished social order based on kin ties (societas) from social order
based on political ties (civitas): The experience of mankind . . . has developed but two plans of government and both were definite and systematic organizations of society. The first and most ancient was social organization, founded upon gentes, phratries and tribes. The second and latest in time was a political organization founded upon territory and upon property. Under the first a gentile society was created, in which the government dealt with persons through their relation to a gens and tribe. These relations were purely personal. Under the second a political society was created, in which the government dealt with persons through their relations to territory, e.g. the township, the county, and the state. These relations were purely territorial. The two plans were fundamentally different. One belongs to ancient society, the other to modern. (1877:62)
Morgan briefly described the organization of society based on sex, reprising his reconstruction of the communal and brother-sister families, and then proceeded to his principal concern: the nature of the gens or, in modern anthropological terms, the lineage. In Morgan’s terms, the gens is a named social group of consanguineal kin (that is, kin related by “blood,” not marriage) descended from a common ancestor (1877:63). Whether matrilineal or patrilineal, the gens (plural: gentes) was the “fundamental basis of ancient society” found in cultures around the world and spanning the ethnical periods from savagery to civilization (Morgan 1877:64). When bound together into groups of two or more gentes—which Morgan called “phratries,” but today are known as “clans”—such kin-based social institutions provided the structure for the distribution of rights, property, and political offices. When a group of gentes or phratries also had a single name for the entire group, spoke a single dialect, and had a supreme government and an identified territory, then social order had reached the level of the tribe (Morgan 1877:102–103). In turn, when tribes coalesced into a single entity, a nation existed.
Thus, Morgan argued that government evolved from promiscuous horde to brother-sister group families, from group families to gens, and then progressively through stages of phratry, tribe, and nation.