The Latin Empire of Constantinople (1204-1261)
On 13 April 1204 Constantinople fell to the Latins. On 9 May 1204 Baldwin I of Flanders was elected emperor and a few days later (16 May 1204) he was crowned in Hagia Sophia in Constantinople.
According to the treaty of distribution of the territories of the Byzantine Empire (Partitio terrarum imperii Romaniae), - of the empire of Romania and 5/8 of Constantinople were awarded to the Latin emperor, whereas the rest - of the empire were distributed among the crusaders and the Venetians and the 3/8 of Constantinople were granted to the Venetians. The Venetian doge was the only one among the crusaders who was exempted from the obligation to pay homage to the Latin emperor and played a decisive role in the election of the Latin archbishop of Constantinople Thomas Morosini. Moreover, as the owner of 3/8 of the empire he could exercise the right of veto in the election of the new emperor.
The first campaigns of the Latins in Asia Minor, in the purpose of conquering the lands that were apportioned to the Latin emperor, resulted in the conquering of a large part of Bithynia (autumn-winter of 1204/1205). The war campaigns of the Latins in Asia Minor continued successfully until the spring of 1207, when they signed with the emperor of Nicaea Theodore I Laskaris a treaty of a two-year truce. On 15 October 1211, the Latins accomplished a significant victory against the Nicaean troops at the Ryndakos river, in Bithynia. In 1214 the treaty of Nymphaeum was signed securing for the Latins the control of the northeastern part of Asia Minor.
The friendly relations between the Latin Empire and the empire of Nicaea were maintained in general until 1222, when the war resumed. In 1224, the Latins suffered a heavy defeat near Poimaninos losing gradually their acquisitions in Asia Minor and in 1225 they signed with the emperor of Nicaea a treaty of truce, by which their acquisitions in Asia Minor were reduced to the region opposite Constantinople, together with environs of Nicomedia. During the same period, the fleet of Nicaea conquered islands in the Aegean Sea that had been awarded to the Latin emperor of Constantinople (Ikaria, Lesbos, Kos and Chios), whereas in 1235 fell the last Latin forts of Asia Minor.
The first military successes of the Franks in Asia Minor (autumn-winter 1204/1205) were overshadowed by serious problems that broke out in the wider region of Thrace, where the local Byzantine lords had entered into alliance with the Bulgarian tsar Ioannitzis (1197-1207). The troops of the tsar invaded Thrace and clashed with the forces of the Latin emperor in the environs of Adrianople on 14 April 1205. The Franks were decimated and the Latin emperor of Constantinople Baldwin I was captured. The new emperor Henry of Flanders (1206-1216) succeeded in retaking many territories in the region of Thrace. In October 1207, Ioannitzis got killed during the siege of Thessalonika. The Bulgarian danger was ward off conclusively on 1 August 1208, when Henry of Flanders defeated the Bulgarians with a military force of 2,000 men.
In the spring of 1209, Henry in his effort to suppress the rebellious movement of the Lombard lords of Thessalonika launched a campaign in Thessaly and in central Greece. In order to secure his rear from a possible attack of the despot of Epirus Michael I Komnenos Doukas (1204-1215), Henry contracted a treaty of alliance with him in the summer of 1209. The attack of Michael I against the Latin kingdom of Thessalonika, in 1210, caused the direct reaction of Henry, who hastened to reinforce the region. Henry demonstrated a great interest in the defence of Thessalonika. However, on 11 June 1216 he passed away, while he was supervising the works for the construction of the city’s walls. After the fall of the Latin kingdom of Thessalonika (1224), Constantinople was menaced directly by the despot of Epirus Theodore I Komnenos Doukas (1215-1230), successor of Michael I of Epirus, when, after a sweeping campaign to Thrace, he reached the walls of Constantinople. The danger was averted for the Latin Empire of Constantinople in 1228, with the treaty of truce with Theodore.
Henry of Flanders was succeeded by Peter Courtenay (1216-1217), who was captured in an ambush of the despot of Epirus, Theodore. The regency was exercised in Constantinople by the Peter’s wife, Yolande, until 1221, when her son Robert Courtenay ascended the throne (1221-1228). After the death of Robert (1228), the regency was exercised by Jean de Brienne (1229-1237) until the successor to the throne Baldwin II (1237-1261) attained majority. The interior situation in the empire, combined with the constant menace coming from the neighbouring empire of Nicaea, forced Baldwin II to embark on a series of journeys to the West, with a view to rekindling the interest in the bad economic and military situation of the Latin Empire of Constantinople, but without success.
In July 1261, Constantinople was virtually divested of its defensive machine, seeing that the Venetian fleet, manned with all the soldiers of the empire, launched a campaign in the Black Sea. Taking advantage of the total absence of military force in Constantinople, the official of Nicaea Caesar Alexios Stratigopoulos, head of a small military force, invaded Constantinople without meeting any resistance. The recapture of Constantinople by the Byzantines of Nicaea put an end to the Latin Empire.