The Middle Ages spanned from 500-1500 AD. After the fall of the Roman Empire, threats of attacks led to the decline of cities and rise of feudalism as a political system with land granted in exchange for loyalty. Manorialism was the economic system of self-sufficient farming estates with little trade. Charlemagne created a large empire and helped revive learning in Europe, though it declined after his death. Europe was weakened by invasions until the rise of the powerful Roman Catholic Church and the Crusades between 1000-1300 AD, but the Black Death plague from 1347-1351 killed one-third of Europe's population and ended feudalism.