Hundreds of years ago, some places in Africa valued glass beads as their money because they were hard to make. In Europe, glass beads were easy to make, and there were lots of them.

One day a European who travelled to Africa said when he got back home:

"Africa will trade us gold and ivory for glass beads."

Enough said. Europeans got on their boats and sailed to Africa.

When they got there, they bought gold and ivory from Africa. After buying other valuable resources, they had nothing left to buy, so they went home.

But now Africa had no resources and millions of glass beads. Now what? They had hyper-inflated money, and no one wanted it. They had to start trading human lives for survival resources. This is how the slave trade began. 

This happened in other countries with sea shells, feathers and rocks (rare in some locations but not others). Hyperinflation causes Slave Trades.