The first europeans to develop trading relationships with west africa were the

The Portuguese.

Portugal sent ships to explore the western coast of Africa already in the early 1400s.  Prince Henry of Portugal (1394-1460) was nicknamed "the Navigator" because of his strong interest in fostering such voyages of discovery.  They were seeking trade and wealth not only with Africa but also possible alternate trade routes to India.  By the 16th century, the Portuguese had begun slave trade as one of their commercial ventures in Africa.