the issue of concubines

[du'a]

(correct me if im wrong) concubines were allowed in islam up until a certain time right? when was the concept of a concubines outlawed if it ever was? is it considered zina? what constitutes a concubine?

 

[diplomaticmuslim]

a concubine is a category of female slave. slavery persisted throughout the world until 1948, when it was finally outlawed by the UN.

among the chief slave traffickers, in the past, were:
Tribes of Israel
Arabs
Holy Roman Empire
Western Europe
United States of America

 

[du'a]

con·cu·bine (kngky-bn, kn-)
n.
1. Law A woman who cohabits with a man without being legally married to him.
2. In certain societies, such as imperial China, a woman contracted to a man as a secondary wife, often having few legal rights and low social status.

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i know... but what about the issue?