The kingdom of Bosnia was, as we have seen, subject to constant incursions on the part of the Turks, whom it was incapable of resisting, for under the reign of King Dabiša and Queen Helena Gruba the Vojvods had risen to power once more, and had become almost independent. Of these the most important were Sandalj Hranić, lord of Hlum, of whom we have already spoken; Hrvoje, Duke of Spalato; and Paul Radinović. Sandalj ruled over a great part of Hlum as far as the Drina. Hrvoje, who has been described as the “Bosnian Warwick,” owing to the number of princes he deposed and set up, ruled over middle Dalmatia, a large part of Bosnia, including the town of Jajce, and some districts of Hlum, including Livno. Paul Radinović was lord of Trebinje, part of Canali, and other lands as far as Prača. His sons, Peter and Radosav, took the name of Paulović. Queen Helena lost her throne owing to a rebellion in 1398 or 1399, and was succeeded by Stephen Ostoja, probably a natural son of Stephen Tvrtko.[339] Ostoja had to depend for his authority on the goodwill of his magnates, but his reign was at first successful. He defeated Sigismund of Hungary, who tried to enforce his claims on Bosnia, and had invaded it at two points. Also on the Turkish frontier things were more peaceful, and, according to Klaić, after the raid of 1398 Ostoja concluded a treaty with Bayazet to support the claims of Ladislas of Naples to the Hungarian throne against Sigismund.[340] Later, Bayazet became still less formidable, as he had to hurry off to Asia to defend his Empire against Timur.