Byzantine continued the Roman Empire's conflict with the Persian Empire. Economically, Byzantium was a central player in the long-distance trade of Eurasia, with commercial links to Western Europe, Russia, Central Asia, the Islamic World, and China. Culturally, Byzantine libraries preserved Greek texts from the golden age of Hellenistic thought at a time when such learning was lost in the West. These texts would later be introduced to the West and Islamic World. Byzantines spread their culture northwards into Slavic lands. In the 9th century, 2 Byzantine missionaries, Cyril and Methodius, developed a writing system for the Slavs based on Greek letters. This allowed the translation of the Bible and spreading of their faith in the Balkans and Russia. Trade circuit connected to other trade networks throughout the rest of Asia, the Indian Ocean, the Middle East, and Europe, doing much to forage of global economy. Forced some people, such as artisans and engineers, to move from one place to another where their skills are needed. Others moved freely as a part of religious traveled tolerated by the Mongols or as part of commercial activity encouraged by the Mongols. Technology, especially from China, medical knowledge, crops, paining, printing, gunpowder, weapons, compass navigation, high temperature furnaces. As China was wealthy, it had no real way to expand overseas, and as China was centralized, when the state decided to stop the voyages, it could do so very quickly. The Europeans, on the other hand, were desperate to break into larger world economy. In Europe, merchants saw economic opportunity, monarchs saw new tax revenues, and the church saw a way to expand their faith. Thus, there were many more push factors in the poorer and isolated Europe than there were in the wealthy and confident China.