Holy Roman Empire. The transformation of Hungary into a Christian state was one of Stephen's principal concerns throughout his reign. Although the Hungarians' conversion had already begun in his father's reign, it was only Stephen who systematically forced his subjects to give up their pagan rituals. His legislative activity was closely connected with Christianity. For example, his First Book of Laws from the first years of his reign includes several provisions prescribing the observance of feast days and the confession before death. His other laws protected property rights and the interests of widows and orphans, or regulated the status of serfs. Many Hungarian lords refused to accept Stephen's suzerainty even after his coronation. The new King first turned against his own uncle, Gyula the Younger, whose realm "was most wide and rich", according to the Illuminated Chronicle. Stephen invaded Transylvania and seized Gyula and his family around 1002 or in 1003. The contemporary Annals of Hildesheim adds that Stephen converted his uncle's "country to the Christian faith by force" after its conquest. Accordingly, historians date the establishment of the Diocese of Transylvania to this period. If the identification, proposed by Kristó, Györffy and other Hungarian historians, of Gyula with one Prokuiwho was Stephen's uncle according to Thietmar of Merseburgis valid, Gyula later escaped from captivity and fled to Bolesław I the Brave, Duke of Poland (r. 992–1025). About a hundred years later, the chronicler Gallus Anonymus also made mention of armed conflicts between Stephen and Boleslav, stating that the latter "defeated the Hungarians in battle and made himself master of all their lands as far as the Danube". Györffy says that the chronicler's report refers to the occupation of the valley of the river Moravaa tributary of the Danubeby the Poles in the 1010s. On the other hand, the Polish-Hungarian Chronicle states that the Polish duke occupied large territories north of the Danube and east of the Morava as far as Esztergom in the early 11th century. According to Steinhübel, the latter source proves that a significant part of the lands that now form Slovakia were under Polish rule between 1002 and 1030. In contrast with the Slovak historian, Györffy writes that this late chronicle "in which one absurdity follows another" contradicts all facts known from 11th-century sources. The Illuminated Chronicle narrates that Stephen "led his army against Kean, Duke of the Bulgarians and Slavs whose lands are by their