From the beginning of his reign, Otto III faced opposition from the Slavs along the eastern frontier. Following the death of his father in 983, the Slavs rebelled against imperial control, forcing the Empire to abandon its territories east of the Elbe river. Otto III fought to regain the Empire's lost territories throughout his reign with only limited success. While in the east, Otto III strengthened the Empire's relations with Poland, Bohemia, and Hungary. Through his affairs in Eastern Europe in 1000, he was able to extend the influence of Christianity by supporting mission work in Poland and through the crowning of Stephen I as the first Christian king of Hungary.