Why was the slave trade called Triangular trade?

It was called the triangular trade because of the triangular shape that the three legs of the journey made.

The first leg was the journey from Europe to Africa where goods were exchanged for slaves. The second, or middle, leg of the journey was the transportation of slaves to the Americas. It was nicknamed the 'middle passage. The third and final leg of the journey, was the transport of goods from the Americas back to Europe.