This chapter details how, in the course of the twentieth century, the position of the Orthodox and Oriental Orthodox Churches weakened markedly—and apparently irreversibly—in some of their historic strongholds, such as Egypt and Palestine, while in most of eastern Europe, Orthodoxy came under severe ideological pressure from communist regimes between 1917 and 1989, only to emerge into the post-Soviet era remarkably intact. Perhaps the most striking feature of Orthodox history during the century is the extent of the global diffusion—yet at the same time tendency to ethnic fragmentation—of Orthodox Christianity. By the close of the century, there were more than 3 million Orthodox Christians in North America, who were subject to at least fifteen different ecclesiastical jurisdictions. The primary reason for such geographical and institutional diffusion was the intercontinental migration of diverse Orthodox populations from various parts of eastern and central Europe, but an important secondary reason was the growing appeal that Orthodoxy exerted on Christians who for one reason or another had become dissatisfied with their former Protestant or Catholic allegiance. By the 1990s, the Orthodox Church was one of the very few churches in western Europe or North America that was displaying steady growth, as a result of both immigration and conversion.