The spread of Christianity into Russia is historically unique in many ways. It occurred at a time when Islam was advancing rapidly out of the Middle East. Yet the Russian monarchy and her people embraced Christianity under the jurisdiction of Constantinople. The reasons for the initial choice of Christianity, rather than Islam, stem from many factors, including geographic, political, economic, moral and cultural factors. Over the subsequent centuries, despite occupation by a foreign power that adopted Islam, Christianity strengthened, partly because it acted as a unifying device of national identity.