I'm not going to go so far as blame Hillary Clinton. However, slavery in some form or another has been going on in North Africa in perpetuity. The migrant issue just made it bigger. It was going when Qadaffi was there as well but it was far more underground. The arabs have been enslaving Africans (and others) for over well over 1500 years to varying degrees of quantity.
That said, the lack of global outcry is alarming. What is more alarming is why the subsaharan African countries aren't boycotting, threatening war, whatever. It's 2018!!