The Battle of Klokotnitsa occurred on March 9, 1230 AD, near the town of Klokotnitsa (in today’s Haskovo District in Southern Bulgaria). In the Battle of Klokotnitsa, the inferior forces of Tsar Ivan Asen II (r. 1218-1241 AD), ruler of the Second Bulgarian Empire (1185-1396 AD), soundly defeated the armies of Theodore Komnenos Doukas (r. 1216-1230 AD), ruler of the Despotate of Epirus, one of the three Byzantine Greek successor states formed after Western European crusaders from the Fourth Crusade conquered Constantinople in 1204 AD, and set up the so called Latin Empire (1204-1261 AD). The Battle of Klokotnitsa is considered one of the most important military victories in the 1400 years of Bulgarian history.
Around 1221–1222, the Bulgarian Tsar Ivan Asen II signed an alliance treaty with Despot Theodore Komnenos Doukas from the Epirus Despotate which allowed Theodore Komnenos to focus on expanding against the Latin Empire by conquering Thessaloniki but also by capturing some Bulgarian territories such as Ohrid in the region of Macedonia. After the death of Latin Emperor Robert of Courtenay (r. 1221-1228 AD), his successor to the throne of the Latin Empire, Emperor Baldwin II was just 11 years old, and the Bulgarian Tsar Ivan Asen II appeared as the most likely choice of a regent for him. As a result, he and the Bulgarian Empire were considered an obstacle by Theodore Komnenos who was aspiring to the throne of Constantinople in order to resurrect the Byzantine Empire. Thus, in early March 1230 AD, Theodore Komnenos invaded Bulgaria with a large army in violation of his alliance with Tsar Ivan Asen II, and without a declaration of war. The Bulgarian Tsar, with a smaller army, marched to meet him surprisingly quickly. On March 9 (March 22), 1230, the their armies met near the town of Klokotnitsa. Tsar Ivan Asen II had the broken alliance treaty to be pierced on his spear and used as a flag. In a battle that lasted till sunset, the Epirotians were completely defeated, and only a small force under the despot’s brother, Manuel Komnenos Doukas, managed to escape. The rest were killed in the battle or captured, including the entire royal court of Epirus and Theodore Komnenos himself.
After the Battle of Klokotnitsa, the Bulgarian Tsar Ivan Asen II released the captured soldiers without any conditions, while the nobles were taken to the Bulgarian capital Tarnovgrad (today’s Veliko Tarnovo). His fame for being a merciful and just ruler went ahead of his march to the lands of Theodore Komnenos, and they were regained to Bulgaria without resistance. These included the territories between the Black Sea, the Aegean Sea, and the Adriatic Sea. The captured Despot Theodore Komnenos was kept as a prisoner in Tarnovgrad for seven years; he was blinded after his involvement in a conspiracy there. He was released in 1237, after the Bulgarian Tsar Ivan Asen II married his daughter Irene, and returned to Epirus where he died in 1253.