It also devastated the Sassanid Persian Empire. Caliph Abu Bakr seized the opportunity to launch military campaigns that overran the Sassanians and captured Roman-held territories in the Caucasus, the Levant, Egypt, and elsewhere in North Africa. Before the Justinian Plague, the Mediterranean world had been commercially and culturally stable. After the Plague, it fractured into a trio of civilizations battling for power: the Islamic Civilization, the Byzantine Empire, and what became known as Medieval Europe. With so many people dead, the supply of workers, many of whom were slaves, was critically short. Landowners had no choice but to lend pieces of land to serfs who work the land in exchange for military protection and other privileges. Thus sowed the seeds of feudalism.