Nigerians formed their own mafia, their thing is to drug people at a friendly bar then steal all their cards and cash. They dump the body in an ally a block away and when you wake up your credit card is maxed and you have no cash. They tried to compete with the Yakuza but businesses would refuse to cooperate so many became toughs and strongmen for the various groups in exchange for getting married (hooker or stripper) to avoid deportation. They're the reason Japan ditched marriage equals citizenship.