The problem lies in their original homeland. They are all escaping murderous regimes of one sort or another. The answer is for the United Nations to identify the two or three worst human rights offenders in Africa and send a multinational force to take over the administration of these countries. People could still vote for leaders, but the police and army would be under UN control and the leaders would be unable to divert aid money to their own purposes. UN would stay there, in numbers that were necessary, until the infrastructure was strong enough that the police and army could not be bribed and controlled by a single dictator. That could take several generations. 
In its present form the UN is useless. It needs to go where it is needed to protect the most vulnerable in these countries. What we are doing right now is not working.