Simplify the following text for a Grade 9 native English-speaking person.
Original: When the last duke of Saxe-Wittenberg died without heir in 1422 , the Emperor Sigismund gave the duchy to Frederick IV of the house of Wettin , Margrave of Meissen and Landgrave of Thuringia , who thereby became Frederick I , Elector of Saxony .
Simplified: When duke of Saxe-Wittenberg died without an heir in 1422 , the Emperor Sigismund gave the duchy to Frederick IV of the House of Wettin . Frederick was already Margrave of MeiÃ en and Landgrave of Thuringia , and then became Frederick I , Elector of Saxony .