National images and international systems

"relevant variables." Just what is relevant and what is not is a matter of judgment of the system-builder, but we think of such things as states of war or peace, degrees of hostility or friendliness, alliance or enmity, arms budgets, geographic extent, friendly or hostile communications, and so on. Having defined our variables, we can then proceed to postulate certain relationships between them, sufficient to define a path for all the variables through time. Thus we might suppose, with Lewis Richardson,2 that the rate of change of hostility of one nation toward a second depends on the level of hostility in the second and that the rate of change of hostility of the second toward the first depends on the level of hostility of the first. Then, if we start from given levels of hostility in each nation, these equations are sufficient to spell out what hapinternational system consists of a group interacting behavior units called "nations" "countries," to whic may someti es be ded certain supra-n tional organizations,