Mahan, of the United States Navy, and Halford Mackinder, the British geographer. Spykman's work is based on assumptions similar to Mackinder, the unity of world politics and the unity of the world sea, but extends it to include the unity of the air. The exploration of the entire world means that the foreign policy of any nation will affect more than its immediate neighbors; it will affect the alignment of nations throughout the world's regions. Maritime mobility opened up the possibility of a new geopolitical structure: the overseas empire. Spykman adopts Mackinder's divisions of the world but renames some: the Heartland the Rimland (analogous to Mackinder's "inner or marginal crescent") the Offshore Islands & Continents (Mackinder's "outer or insular crescent") Heartland At the same time, even if he gives credit to the strategic importance of maritime space like Mackinder, he does not see it as a region that will be unified by powerful transportation or communication infrastructure in the near future. As such, it will not be in a position to compete with US sea power. Spykman agrees that the Heartland offers a uniquely-defensive position, but that is all Spykman grants its occupier. While the USSR encompassed a great expanse of land, its arable land remained in a small portion of its territory, mostly in the West. Indeed, the Soviet's raw materials were largely located to the West of the Ural Mountains as well. Since the political and material center of gravity was in the Western part of the USSR, Spykman sees little possibility of the Soviets exerting much power in Central Asia. Still, the Soviet Union was to remain the greatest land power in Asia and could be a peacekeeper or a problem. Rimland The Rimland (Mackinder's "Inner or Marginal Crescent") sections: the European coast land; the Arabian-Middle Eastern desert land; and, the Asiatic monsoon land. While Spykman accepts the first two as defined, he rejects the simple grouping the Asian countries into one "monsoon land." India, the Indian Ocean littoral, and the culture of India had a geography and civilization separate from the Chinese lands. The Rimland's defining characteristic is that it is an intermediate region, lying between the Heartland and the marginal sea powers. As the amphibious buffer zone between the land powers and sea powers, it must defend itself from both sides, the cause of its fundamental security problems. Spykman's conception of the Rimland bears greater