Before the inception of Islam — in fact, even after its rise — the institution of slavery prevailed over a large part of the world. On examining the history of ancient Rome, Greece, Egypt and Persia, we find that slave labour was used as the instrument of economic progress in all of these countries.
Slavery was made possible basically through two channels. One way was when countries at war with neighbouring states captured the citizens of their opponents and turned them into slaves. For example, when the opportunity arose, the Romans would capture the Persians as slaves, or the other way around. Thus, each side would enslave people of the other side, expecting thereby to deal a blow to the opponent’s political power. The second way to enslave people was to capture women and children from the backward parts of the world. While the first means of enslaving people was adopted at opportune occasions, the second method became a sustained practice over time.
In fact, that approach to slavery continued well into the 18th century when hoards of West Africans were brought over into the United States. Although slavery no longer exists in that country, some 20–30 million Americans are descendents of people who were brought as slaves.
The main motivation behind slavery in advanced countries was to further their economic might through cheap slave labour. The slaves were exploited in different ways. They were assigned to work in factories, or ships, or any other work involving heavy manual tasks required for economic development. Similarly, slave labour was used on plantations in order to minimise production costs and to maximize profit.