however, is always found between the members of the same species.
Usually this conflict within the species is a competition between
groups. The human species exactly illustrates these statements.
Primitively its great conflict was with other species of animals. The
supremacy of man over the rest of the animal world was won only after an
age-long conflict between man and his animal rivals. While this conflict
went on there was apparently but little struggle within the species
itself. The lowest groups of which we have knowledge, while continually
struggling against nature, are rarely at war with one another. But after
man had won his supremacy and the population of groups came to increase
so as to encroach seriously upon food supply, and even on territorial
limits of space, then a conflict between human groups, which we call
war, broke out and became almost second nature to man. It needs to be
emphasized, however, that the most primitive groups are not warlike, but
only those that have achieved their supremacy over nature and attained
considerable size. In other words, the struggle between groups which we
call war was occasioned very largely by numbers and food supply. To this
extent at least war primitively arose from economic conditions, and it
is remarkable how economic conditions have been instrumental in bringing
about all the great wars of recorded human history.

The conflict among human groups, which we call war, has had an immense
effect upon human social evolution. Five chief effects must be noted.

(1) Intergroup struggle gave rise to higher forms of social
organization, because only those groups could succeed in competition
with other groups that were well organized, and especially only those
that had competent leadership.

(2) Government, as we understand the word, was very largely an outcome