The problem is indeed that any one nation opening borders would be somewhat overwhelmed. In reality the solution is to open borders of all nations everywhere. This is not going to happen for a long, long time, if at all. However, bear in mind that it is not common for people to actually want to emigrate. For example, most immigrants from Eastern Europe to the West only actually want to go for a few months to earn some money so their family has more security when they go back. People don't want to leave their homes much of the time - they go through necessity. If they were allowed to come in, earn a few months wages, and go back home, both nations would benefit. In this particular instance, Spain would have people to do the less savory jobs, whilst the African nations would be bringing in desperately needed wealth. Then these people can start new businesses of their own in Africa, leading to more jobs and wealth over there.