Thus, western Christianity played a major role in advancing and perpetuating slavery.
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Toadies licking the boots of European warlords played a major role in slavery.
When the bible was widely printed and read, agitation for the end of slavery came about amazingly quickly. The demand for reform ( not only slavery) but of the abuses of the warlords and their religious toadies rose up spontaneously from the common people.
It is Christianity and it scriptures, when freely available to all, that tames warlords, promotes freedom, trust in your neighbor, and encourages respect for all people as children of God equal in His sight.
I don't know where you are getting your ideas from. The printing press was invented in Europe in 1453 (15th century) and last vestiges of slavery were abolished in Europe and the US in the latter half of the 19th century, more than 400 years later.
In addition to that, there was no need to wait the printing press: there were tens of thousands of hand-made copies of the Bible available (the so-called 'majority text').
And even after they were printed en masse, most of the people were illiterate and couldn't read them, let alone afford them!