The Byzantine–Bulgarian wars were a series of conflicts fought between the Byzantines and Bulgarians which began when the Bulgars first settled in the Balkan peninsula in the 5th century, and intensified with the expansion of the Bulgarian Empire to the southwest after 680 AD. The Byzantines and Bulgarians continued to clash over the next century with variable success, until the Bulgarians, led by Krum, inflicted a series of crushing defeats on the Byzantines. After Krum died in 814, his son Omurtag negotiated a thirty-year peace treaty. In 893, during the next major war, Simeon I, the Bulgarian emperor, defeated the Byzantines while attempting to form a large Eastern European Empire, but his efforts failed. In 971 John I Tzimiskes, the Byzantine emperor, subjugated much of the weakening Bulgarian Empire, facing wars with Croatians, Magyars, Pechenegs and Russians, by defeating Boris II and capturing Preslav, the Bulgarian capital. Constantinople under Basil II completely conquered Bulgaria in 1018 as a result of the 1014 Battle of Kleidion. There were rebellions against Byzantine rule from 1040 to 1041, and in the 1070s and the 1080s, but these failed. In 1185, however, Theodore Peter and Ivan Asen started a revolt, and the weakening Byzantine Empire, facing internal dynastic troubles of its own, was unable to prevent the revolt from being successful. After the Fourth Crusade conquered Constantinople in 1204, Kaloyan, the Bulgarian emperor, tried to establish friendly relations with the crusaders, but the newly created Latin Empire spurned any offer of alliance with the Bulgarians. Because of his cold reception, Kaloyan allied with the Nicaeans, one of the Byzantine states created after the fall of Constantinople, instead, which reduced the crusaders’ power in the area. Even though his nephew Boril allied with the Latin Empire, Boril’s successors sided with the Nicaeans, despite a few continuing attacks from them. After the Latin Empire collapsed, the Byzantines, taking advantage of a Bulgarian civil war, captured portions of Thrace, but the Bulgarian emperor Theodore Svetoslav retook these lands. The Byzantine-Bulgarian relations continued to fluctuate until the Ottoman Turks captured the Bulgarian capital in 1393 and the Byzantine in 1453.