 Under Radu I and his successor Dan I, the realms in Transylvania and Severin continued to be disputed with Hungary.Basarab was succeeded by Nicholas Alexander and Vladislav I. Vladislav attacked Transylvania after Louis I occupied lands south of the Danube, conceded to recognize him as overlord in 1368 but rebelled again in the same year.Vladislav's rule also witnessed the first confrontation between Wallachia and the Ottoman Empire, a battle in which Vladislav was allied with Ivan Shishman.