The western half of the European Christian world followed a rather different path than that of the Byzantine Empire. For much of the third-wave millennium, it was distinctly on the margins of world history, partly because of its geographic location at the far western end of the Eurasian landmass. Thus it was at a distance from the growing routes of world trade—by sea in the Indian Ocean and by land across the Silk Roads to China and the Sand Roads to West Africa. Not until the Eastern and Western hemispheres were joined after 1500 did Western Europe occupy a geographically central position in the global network. Internally, Europe’s geography made political unity difficult. It was a region in which population centers were divided by mountain ranges and dense forests as well as by five major peninsulas and two large islands (Britain and Ireland). However, its extensive coastlines and interior river systems facilitated exchange within Europe, while a moderate climate, plentiful rainfall, and fertile soils enabled a productive agriculture that could support a growing population.