Pretty much this. Slavery was common the world over. The major difference was that the British empire and others industrialised it on a scale not seen before. But in most cultures of the time it was pretty accepted. So it's all very well us going 'slavers disgusting people'. But to them, to the slaves (many of who lived in cultures that had enslaved people themselves), it was the norm of the time. And I find it hard to sit on a high horse and condemn people in the past for actions which were seen as normal then. Certainly modern day slavery still exists though and it isn't particularly the West who are involved.
Aaaactually, percentage wise, slavery from the 15th-18th century (where most of the slave trade happened) was much lower than in the past (except for a small period of time in the early 14th century where the pope forbid slavery and then the Spaniards found the Carribean so he kind of went 'fuck it'). The big difference is that, unlike in the past, most of the slaves didn't come locally or from the surrounding areas but from far-away lands to be sold to far-away lands. Still, in Ancient Greece (where slave culture is one of the best recorded), slaves made up about 30% of the Athenian republic population and Ilotes (slaves, essentially) made up about 60% (!!!) of the Spartan population. In the US, during the civil war, Slaves were less than 10% of the total population and the number dropped when the deportations to Liberia happened.
Not to mention stuff like the serfdom in Russia and Romania that was essentially slavery and included up to 90% of the actual population and it lasted until the abolition of serfdom in the early 20th century.
Or how about the Egyptians, that had, under law, forced labor for the benefit of the state at least a few months a year (unless you were a priest or a noble, which less than 5% of the population was). The pyramids didn't build themselves.
So, huge industrial scale? No. More systematic way? Absolutely yes. But even that wasn't unprecedented. I will only remind of the Christian slave trade by the Khans of the black sea in the 15-16th century. They sold upwards to 3 million Christian slaves (mostly Slavs, from which the bloody word "slave" comes from) to the Ottoman empire that, in turn, sold them to the rest of the Arab nations. It was said that during the height of the Ottoman empire you could find Hungarian slaves in freeking Oman. And it wasn't just them. The Barbari coast pirates raided until the 18th century and there were reports of even looting villages in Iceland. Barbari coast, in case you are wondering, was the old name of north-west African coast, ie Morroco, Algeria etc.
