How come Europe were able to overtake and transport so many slaves from Africa in ancient times? What in history brought about the advanced developments in weaponry or whatever that caused these caucasian intruders to be able to carry out such horrible deeds for close to one thousand years?

When and how in history was this «upper hand» in technology, weaponry and/or society brought about that enabled this to go down the way it did?

I know this question is dumb and poorly phrased but I'm reading a book on the Libyan boat refugees and they're still traveling by the same trans-Saharan route that was used for slave trades for almost a millenium. And I wonder when did the world evolve from (ALL of) our ancestors chillin in the seas and trees to this division in race, which then later advanced to the point that certain European countries were able to carry out this shit and strongarm a whole continent for almost a 1000 years