As we saw in the first chapter, nature had clearly defined the paths by which America might be found. The time when the discovery would be made was almost as definitely determined by events in the Old World. For countless centuries, Europe, by many routes and through many intermediaries, had traded with the vaguely localized countries of the Orient. Throughout the Middle Ages, not only had she been dependent on the East for most of her luxuries, but many of these, from long usage, had become necessities.[47] About the beginning of the fourteenth century, this commerce, “the oldest, the most extensive, and the most lucrative trade known to Europe,” began to be interfered with by the internal changes in the East, mainly due to conquests by the Ottoman Turks. Beginning about 1300, marked by the fall of Constantinople in 1453, and continuing until all the seaports of the eastern Mediterranean, including those of Egypt, were in their possession by 1522, the process was a gradual one. At first uneasy, then alarmed, finally facing commercial ruin by the almost complete strangulation of her Oriental trade, Europe struggled frantically against geographical conditions, in her efforts to find a new and unimpeded route to the East. Footnote 47: _Cf._ E. P. Cheyney, _European Background of American History_ (New York, 1904), pp. 3-41. During the latter part of the same period, geographical science had been making many strides; while the theory of the earth's sphericity had been held, by some at least, since the days of Plato. After nearly two thousand years, motives developed which led men to turn that idea into action by use of the new discoveries, and in one generation Columbus sailed west to America, and Da Gama east to India, and Magellan circumnavigated the globe. The thought advanced by philosophy, denied by common sense, and fought by the Church, finally wrought the greatest change yet known in the world's history through the commonplace necessities of trade.