How did slavery affect world history?
Nowadays the word "slavery" is mostly associated with the United States in the period before the Civil War. However, slavery originates from the prehistoric times, and probably the most famous state which had build its prosperity on slave labor (among other things) was Ancient Greece: the civilization which has in many ways shaped the world as we know it today. Slave labor provided ancient Greeks with a large amount of free time that was spent on philosophy, arts, sciences, and socio-political life (the word "democracy," as well as the very principle of running a state based on the opinion of all of its citizens, originates from Ancient Greece). As for the American slavery, it was the necessary premise for the Civil Rights movement and the proclamation of equality between people of different races.