At the close of the twelfth century the internal situation in Bulgaria was deteriorating. Taxes had been increased, and the burden borne by the peasants became still heavier. The feudal lords openly began to proclaim their independence from Byzantium, whose empire was by now steadily declining. Bulgaria was surrounded by its enemies: the Ottoman Turks, the Magyars, and the Normans. In 1183 the Magyars invaded, penetrating as far as Sofia. Realizing the vulnerability of the Byzantine Empire, the Bulgarians rebelled under the leadership of two brothers, Asen and Peter. The brothers first liberated northeastern Bulgaria and then proceeded into Thrace, where they were opposed by Isaac Angel, then emperor of Byzantium. In 1187 a peace treaty was concluded in which Byzantium conceded autonomy to Bulgaria. Despite the peace treaty, however, the Bulgarians continued to wage war against the empire, hoping to regain northern Bulgaria and Macedonia--a contested territory and bitterly disputed issue throughout Bulgarian history. In 1201 the empire again concluded a peace treaty with the Bulgarians, ceding all of northern Bulgaria and a large part of Macedonia. Eventually, in 1207 Constantinople recognized the complete independence of Bulgaria, and Bulgarian freedom was firmly established. This new-found independence, however, did not extend to the Bulgarian church, which was still under the aegis of the empire. For that reason Kaloyan, the Bulgarian ruler, negotiated with the Roman pope, Innocent III, in order to ally the Bulgarian church with the church of Rome. The motives of Rome and those of Kaloyan were similar: to isolate the influence of Byzantium from Bulgaria. In 1204 Kaloyan was crowned king by the papal nuncio in Turnovo. Although this union lasted only briefly, it served the purpose for which it was designed, and Bulgaria was effectively cut off from Byzantium. During the thirteenth century the Holy Roman Empire replaced the Byzantine Empire on the borders of Bulgaria, and Byzantine aggression was replaced by that of the Holy Roman Empire. When Rome declared war on Bulgaria, the Bulgarians invaded Thrace, defeating the crusaders at Adrianople in 1205. The reestablishment of the Bulgarian patriarchate in 1235 represented the end of the short-lived alliance between the Bulgarian church and Rome. Under the reign of Ivan Asen II in the mid-thirteenth century peace was again restored, and the country once more extended its territories. The Bulgarians succeeded in capturing eastern Thrace, the Aegean coast, Albania, and Macedonia. Bulgarian territory at this time was as great as under the reign of Tsar Simeon; with these conquests Bulgaria became the largest state in the Balkans. The country was now surrounded by three seas--the Black Sea, the Aegean Sea, and the Adriatic Sea--opening the country's doors to foreign trade and culture.