An examination of fact shows that where groups of the patriarchal type
fall into regions permitting considerable growths of population, but
having physical structures which impede the centralisation of power,
compound political heads will arise and for a time sustain themselves
through co-operation of the two factors, independence of local groups,
and need for union in war. Thus, as Mommsen says, primitive Rome was
rather an aggregate of urban settlements than a single city. Not only do
conditions determine the various forms which compound heads assume, but
conditions determine the various changes they undergo. They may be
narrowed by militancy, or they may be widened by industrialism.