Economically, the substitution of Turkish for Byzantine rule was a benefit to the Greek industrial population, who were better protected against foreign competition than they had ever been. Customs duties were arranged by an ad valorem scale, under which the Italian merchants were taxed four and a half times as much as the native Christians, although these, in turn, paid more than the Moslem traders who were favored by the Ottoman government. The Greek parts of the Empire entered upon an era of prosperity such as had not been seen since before the Latin conquest of Constantinople. For example, a large colony of Greeks established themselves at Ancona, where, in 1549, they transacted business to the annual value of 500,000 ducats. Moreover, the persecution of the Moors and Jews of Spain brought much capital into Ottoman territory; soon there were numbered 30,000 Spanish Jews at Constantinople, and 15,000 to 20,000 at Salonica. On this commercial basis the national renascence of the Greek peoples was founded. The landed proprietors of their own race mostly became Moslems, while their scholars and literary men found a refuge in the Occident; but the traders made and kept a place for themselves. Hence there was created a new center in which the old ideals of an independent Greek nationality could grow. The Slav peoples were much worse off than the Greek population, because over their provinces were scattered Turkish garrisons, and through them passed the roads used by the Sultan for the interminable expeditions into Hungary. They retained fewer traces of autonomous existence, and their clergy were more ignorant than the Greek. The higher ecclesiastical positions were never bestowed on Slavs, and their landed gentry mostly became Moslem. The Roumanians, who were more remotely situated, preserved, under the form of vassalage, a complete national organization. They paid a moderate tribute, and were obliged to furnish military contingents, but there were no Turks in their territory, and no mosques were built among them. Wallachia and Moldavia, in the time of Souliman, made more than one attempt to throw off Turkish rule, but both principalities were compelled to submit before the middle of the sixteenth century. The Turkish conquest of North Africa begins, strictly speaking, with the resistance of the Moslem Berber tribes and princes to the extension of Spanish influence over the African Mediterranean coast towns. This was a primary object of Charles V, who was bent on following up, by his control of sea power, the expulsion of the Moors from Spain. After many vicissitudes, Kheir-ed-Din, who had a powerful rival supported by the Spaniards, became King of Algiers. He turned to ask help from the Sultan of Constantinople, Selim, and he offered, in return, to become his vassal and to incorporate his small kingdom as an integral part of the Ottoman Empire.