Simplify the following text for a Grade 7 native English-speaking person.
Original: Saxe-Altenburg thereafter remained part of Saxe-Gotha-Altenburg until the extinction of that house in 1825 , when Gotha and Altenburg were split up , with Gotha going to the Duke of Saxe-Coburg-Saalfeld and Altenburg to the Duke of Saxe-Hildburghausen , who in exchange gave up Hildburghausen to the Duke of Saxe-Meiningen .
Simplified: Saxe-Gotha-Altenburg was split up . Gotha was given to the Duke of Saxe-Coburg-Saalfeld and Altenburg to the Duke of Saxe-Hildburghausen , who in exchange gave up Saalfeld and Hildburghausen to the Duke of Saxe-Meiningen .