With whom did the kingdoms in west africa trade?

The main items traded were gold and salt. The gold mines of West Africa provided great wealth to West African Empires such as Ghana and Mali. Other items that were commonly traded included ivory, kola nuts, cloth, slaves, metal goods, and beads.

by improved communication.

well that depends on how deep the hole is. you'd first go through te crust of the earth, then the upper mantle, then the lower mantle then the outer core, then the inner cor then you'd be stuck in the core to melt.