During the early medieval Islamic expansion in the seventh to eleventh centuries, al-Hind (India and its Indianized hinterland) was character­ized by two organizational modes: the long-distance trade and mobile wealth of the peripheral frontier states, and the settled agriculture of the heartland. These two different types of social, economic, and political organization were successfully fused during the eleventh to thirteenth centuries, and India became the hub of world trade. During this period, the Middle East declined in importance, Central Asia was united under the Mongols, and Islam expanded far into the Indian subcontinent. Instead of being devastated by the Mongols, who were prevented from penetrating beyond the western periphery of al-Hind by the absence of sufficient good pasture land, the agricultural plains of North India were brought under Turko-Islamic rule in a gradual manner in a conquest effected by professional armies and not accompanied by any large-scale nomadic invasions.