Leiningen-Westerburg was formed in 1467, when the last Landgrave of Leiningen died childless and Leiningen passed to his sister Margaret, who was married to Reinhard III of Westerburg.
The formation of Leiningen-Westerburg occurred in 1467 due to the death of the last Landgrave of Leiningen without heirs, with his sister Margaret inheriting the land and being married to Reinhard III of Westerburg.