Battle of Adrianople (1205) in the context of "Enrico Dandolo"

The Second Bulgarian Empire (Middle Bulgarian: Ц(а)рьство бл(ъ)гарское; Modern Bulgarian: Второ българско царство, romanized: Vtoro Balgarsko Tsarstvo) was a medieval Bulgarian state that existed between 1185 and 1422. A successor to the First Bulgarian Empire, it reached the peak of its power under Tsars Kaloyan and Ivan Asen II before gradually being conquered by the Ottomans in the late 14th century.

Until 1256, the Second Bulgarian Empire was the dominant power in the Balkans, defeating the Byzantine Empire in several major battles. In 1205, Emperor Kaloyan defeated the newly established Latin Empire in the Battle of Adrianople. His nephew Ivan Asen II defeated the Despotate of Epiros and made Bulgaria a regional power again. During his reign, Bulgaria spread from the Adriatic to the Black Sea and the economy flourished. In the late 13th century, however, the Empire declined under constant invasions by Mongols, Byzantines, Hungarians, and Serbs, as well as internal unrest and revolts. The 14th century saw a temporary recovery and stability, but also the peak of Balkan feudalism as central authorities gradually lost power in many regions. Bulgaria was divided into three parts on the eve of the Ottoman invasion.

Baldwin I (Dutch: Boudewijn; French: Baudouin; July 1172 – c. 1205) was the first Emperor of the Latin Empire of Constantinople; Count of Flanders (as Baldwin IX) from 1194 to 1205 and Count of Hainaut (as Baldwin VI) from 1195 to 1205. Baldwin was one of the most prominent leaders of the Fourth Crusade, which resulted in the sack of Constantinople in 1204, the conquest of large parts of the Byzantine Empire, and the foundation of the Latin Empire. The following year he was defeated at the Battle of Adrianople by Kaloyan, the emperor of Bulgaria, and spent his last days as a prisoner.

The struggle for Constantinople was a complex series of conflicts following the dissolution of the Byzantine Empire in the aftermath of the Fourth Crusade in 1204, fought between the Latin Empire established by the Crusaders, various Byzantine successor states, and foreign powers such as the Second Bulgarian Empire and Sultanate of Rum, for control of Constantinople and supremacy within the former imperial territories.

At the time of the Fourth Crusade, the Byzantine Empire was already divided by internal revolts. In the aftermath of the Crusader sack of Constantinople, the empire was dissolved into a patchwork of territories held by various pretenders and warlords. The former Byzantine emperors Alexios III and Alexios V both aspired to retake the capital, though were defeated by the Latins. The early years after 1204 saw the rise and fall of numerous Byzantine statelets; the Latins managed to defeat warlords such as Leo Sgouros but were unable to halt the formation of the more well-organized rump states of the Empire of Nicaea, Empire of Trebizond, and Despotate of Epirus. The prospect of a potential swift Latin conquest of the entire former empire's territories effectively ended when the Bulgarian ruler Kaloyan defeated the Latin army at the Battle of Adrianople (1205).

Theodore I Komnenos Laskaris or Lascaris (Greek: Θεόδωρος Κομνηνὸς Λάσκαρις, romanized: Theodōros Komnēnós Láskaris; c. 1175 – November 1221) was the first emperor of Nicaea—a successor state of the Byzantine Empire—from 1205 to his death. Although he was born to an obscure aristocratic family, his mother was related to the imperial Komnenos clan. He married Anna, a younger daughter of Emperor Alexios III Angelos in 1200. He received the title of despot before 1203, demonstrating his right to succeed his father-in-law on the throne.

The Fourth Crusade forced Alexios III to flee from Constantinople in 1203. Theodore was imprisoned by the crusaders (commonly referred to as "Latins" by the Byzantines), but he escaped. After crossing the Bosporus into Asia Minor (in present-day Turkey), he started to organise the local Greeks' resistance against the Latins in Bithynia in his father-in-law's name. He concluded an alliance with the Seljuq sultan of Rum, but he could not stop the Latins' expansion. Neither could he prevent a claimant to the imperial throne, Alexios Komnenos, from establishing a Byzantine successor state, the Empire of Trebizond, in northern Asia Minor. Theodore's position consolidated only after Tzar Kaloyan of Bulgaria inflicted a crushing defeat on the Latins in the Battle of Adrianople (in Thrace) in 1205.

Louis I of Blois (1172 – 14 April 1205) was Count of Blois from 1191 to 1205. He is best known for his participation in the Fourth Crusade and later prominent role in the Battle of Adrianople.