If you wish to keep slaves, you must have all kinds of guards. The cheapest way to have guards is to have the slaves pay taxes to finance their own guards. To fool the slaves, you tell them that they are not slaves and that they have Freedom. You tell them they need Law and Order to protect them against bad slaves. Then you tell them to elect a Government. Give them Freedom to vote and they will vote for their own guards and pay their salary. They will then believe they are Free persons. Then give them money to earn, count and spend and they will be too busy to notice the slavery they are in.