CAMBRIDGE, Mass. — HORACE GREELEY, Napoleon Bonaparte and Cecil Rhodes may seem strange bedfellows, but they all agreed that territorial, political and economic size was critical to a country’s success. They wanted more land — in the West, in Europe or overseas. In 1904, Halford Mackinder, an Oxford geographer, told an august assemblage at the Royal Geographical Society that the country that controlled the Russian “heartland,” a frostbitten Central Asian steppe, would dominate “the world island” — the combined territory of Europe and North Asia — and in time come to rule the world. A centrally located piece of territory like the Russian plain, Mackinder argued, could be expanded West and East without the need for naval power.