The mere gathering of individuals into a group does not constitute them a society. A society, in the sociological sense, is formed only when, besides juxtaposition there is cooperation. So long as members of the group do not combine their energies to achieve some common end or ends, there is little to keep them together. They are prevented from separating only when the wants of each are better satisfied by uniting his efforts with those of others, than they would be if he acted alone.
Cooperation, then, is at once that which can not exist without a society, and that for which a society exists.
Herbert Spencer, Principles of Sociology, Vol. II, Part V: Political Institutions, Chapter Two, “Political Organization in General” (1898).