Though this theory predicts that variations in technology are
the most important single determinant of variations in distribution, it
does not hypothesize that they are the only determinant. Three others
are specifically singled out: (1) environmental differences, (2) variations
in the military participation ration, (3) variations in the degree of constitutionalism.
In addition, since this is not a closed theory, it is assumed that other
factors also exercise an influence (1966, p.90).