The causes of the Muscovite Civil War waged in the second quarter of the 15th century are still disputed. No small part, however, was played by Dmitri Donskoi's will, which ran contrary to Rurikid dynastic custom whereby the throne would pass from an elder brother to a younger one (agnatic seniority), rather than from father to son (primogeniture). The testament provided for the accession of his son, Vasily I, which was still in keeping with the tradition of lateral succession since Vasily was the eldest of his generation.