International politics, like nature, is a system of processes. There are no simple causes and effects of historical developments. The record of the past tends to determine the present — until circumstance intervenes. Peoples, like individuals, are at the mercy of what is called chance, and an apparently meaningless combination of circumstances may frustrate the culmination of long-developed tendencies. Tendency is conservative of past forms, and circumstance may appear formless, but their balanced interplay is the source of novel forms. It is only within the frame of reference of these three terms — tendency, circumstance and novelty — that forecasting future developments can derive its warrant from an exact science of prediction. The basic conflict between the United States and the Soviet Union is the central issue of world politics. Sir Halford Mackinder's celebrated theorem — the juxtaposition of the continental empire of Eurasia and the Oceanic Powers, and the contest over the vast rimland interposed be-between the “heartland” and the littoral of Eurasia — is today as brilliant a summation of the world strategic problem as it was forty years ago when it was first propounded.