The pogrom greatly accelerated the emigration of the city's ethnic Greeks to Greece.The population of Istanbul began to rapidly increase in the 1970s, as people from Anatolia migrated to the city to find employment in the many new factories that were built on the outskirts of the sprawling metropolis. This sudden, sharp rise in the city's population caused a large demand for housing development, and many previously outlying villages and forests became engulfed into the greater metropolitan area of Istanbul.[60] As a capital of empires, the city was not only an administrative, but also a religious center. The Patriarchate of Eastern Christians has been headquartered here since its establishment, and the largest early churches and monasteries of the Christian world rose in this city on top of the pagan temples. Within a century after the city was conquered, it was enriched with mosques, palaces, schools, baths and other architectural monuments that gave it a Turkish character, while some of the existing churches in ruins were repaired, altered and converted into mosques.Between the 16th century when the Ottoman sultans acquired themselves the title of the "Caliph of Islam" and 1924, the first year of the Republic, Istanbul was also the headquarters of the Caliphate. More Jews settled in Istanbul than any other port, and here they built themselves a new and happy life after they were rescued from Spain by the Turks in the 15th century. Istanbul has always been a city of tolerance where mosques, churches and synagogues existed side by side. The city was adorned with a large number of dazzling and impressive works even during the period of decline of the Ottomans. During this time, the influence of European art made itself felt in the new palaces, while the northern slopes of the Golden Horn, Galata and Beyoglu districts assumed a European character. Even when the Empire, which was a party to World War I, collapsed and the young Republic that replaced it moved the capital to Ankara, Istanbul did not lose its significance. The haphazard development that began in the years following World War II and accelerated in the 1950s has unfortunately had a negative impact on the fabric of the old city, and while old wooden houses disappeared rapidly, concrete buildings proliferated.