Maria, that's not quite the oldest, largest and deepest system. That distinction actually belongs to Islam. The 'Christian' doctrine of 'discovery' was formulated in the 15th century in the wake of, and very definitely derived from, the Muslim doctrine that everyone else's property, labor and womenfolk belonged of right to Muslims. This means animists, Christians, Jews, Zoroastrians etc. And that doctrine has been in Islam from its beginning. And some imams preach it even now and they are not necessarily a 'fringe' group.

Arab Muslims are also the world's longest and bloodiest slave traders. Their African slave trade probably continues even now under the law's radar. No need to take my word for any of this; google John Azumah Adembillah and see what he has to say in his seminal work, The Legacy of Arab Islam in Africa, for starters.

Remember that Constantinople fell to the Turks in 1453.