What were the negative consequences of using concessionary companies?

Concessionary companies are most typically private European businesses lured to make investments of capital and manpower in Africa in return for a grant (or concession) of land, over which it gained privileged rights of exploitation. The negative consequences are simply rampant exploitation and destruction of indigenous people and cultures. We see this at work with the Igbo although Achebe is not totally unsympathetic to them.