In a paper presented to the Royal Geographical Society in 1904, Mackinder argued that the era of exploration, which he termed the Columbian Epoch, was ending, and that the world was becoming a “closed political system.”2 At the same time, he warned, technology (particularly the development of intricate rail networks) was again making it possible for the Heartland – the core of Eurasia, the place from which, in previous centuries, wave after wave of nomadic invaders threatened the European Rimland – to menace the seapowers of Western Europe. In short, Mackinder believed that a long era was coming to an end, and that a new age, filled with peril, was being born.