Articles from alislam.org:
Measures to End the Institution of Slavery
It should be remembered that the basic source of unnatural and iniquitous treatment — which existed since time immemorial and which Islam brought to an end — was the institution of slavery. It may be not be possible for people today to appreciate the intimate link between slavery and the rise of global commerce and economy; indeed, this is the reason that Islam put a stop to the practice of slavery.
Role Played by Slave Labour in World Economy
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.
SOURCE: https://www.alislam.org/library/book/economic-system-islam/measures-end-institution-slavery/
BOOK REVIEW:
Islam and Slavery
by Hazrat Mirza Bashir Ahmad, M.A. (ra)
In Islam and Slavery, Hazrat Mirza Bashir Ahmad(ra) writes a preeminent treatise on how Islam came to not only end the practice of human slavery, but also to break down the institutional structures and prejudices that uphold slavery. Citing the Qur’an and the exemplary life of Prophet Muhammad(sa), Islam and Slavery masterfully addresses the allegations of critics of Islam, and the behaviors of extremist clerics. The author demonstrates that in Islam the only slavery is one of a worshiper’s submission to God—never of a person over another.
SOURCE:
Prohibition of Unjust Forms of Slavery
In both of the above-mentioned forms, slavery denied equality in treatment to a cross-section of mankind. Islam categorically prohibited both channels of enslaving people. The Holy Quran says:1
Meaning that: It was not lawful for any Prophet before you, nor is it for you, to take prisoners without engaging in a war. If there is a war — and that too, religious — prisoners can be captured in the battlefield.
The condition laid down in this verse does not permit anyone to imprison the civilian population of any country where war has not been declared. Nor does it permit enslaving any citizen of the opponent who has not been part of the attacking force. The imprisonment of those who actively engage in combat is allowed because they would otherwise go back to join forces in attack.
Then Allah says in these verses that: 
‘You desire the frail goods of this world’ meaning: O Muslims, do you desire to behave like other nations and enslave their people to augment your power 
nay, Allah does not want you to follow other nations. He wants to guide you to the course that is better for you in the end and entitles you to win Allah’s pleasure. God reminds Muslims that nearness to God is better than any worldly gain. And God decrees that it is better for you that you do not take any prisoners except when war is imposed on you.
This rule was strictly enforced in the early days of Islam. During the reign of Hazrat Umar(ra), a deputation from Yemen came and complained that, before the advent of Islam, they had been made into slaves without any cause by a neighbouring Christian tribe. Hazrat Umar(ra) replied that though the event took place before the Muslims were in power, he would look into the case and have them set free if their complaint was borne out by facts. In contrast to this enlightened Islamic stand, the Europeans continued to use slavery for advancing their trade and agriculture until the nineteenth century.
There is no doubt that some instances of the un-Islamic custom of slavery can be found in Islamic history; but slavery was never practised to promote domestic industry or trade.
1 Surah al-Anfal, 8:68, (publishers)
Categories: Ahmadiyyat: True Islam, Arab World, Asia, Islam