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).