The three-fifths clause
Back in the day when the 13 colonies were being cobbled together into the United States a strange issue of slavery became an overriding issue for the Southern States. The population growth was in the New England States down through New York and the Southern States were fearful that they would be outvoted on the issue of slavery which was the backbone of their economy. The compromise that settled the issue was the called the 3/5 rule.