In 1195 Isaac II was deposed and blinded by his brother Alexius III. The Westerners, who had again blamed the failure of their Crusade on the Byzantines, saw ways of exploiting the situation. The emperor Henry VI had united the Norman kingdom of Sicily with the Holy Roman Empire. He inherited the ambitions of both to master Constantinople, and his brother, Philip of Swabia, was married to a daughter of the dethroned Isaac II. Alexius bought off the danger by paying tribute to Henry, but Henry died in 1197. The idea had now gained ground in the West that the conquest of Constantinople would solve a number of problems and would be of benefit not only to trade but also to the future of the Crusade and the church. In 1198 Innocent III was elected pope. The new rulers of Hungary, Serbia, and Bulgaria all turned to him for the recognition of the sovereignty that Byzantium would not give them.

It was under Innocent’s inspiration that the Fourth Crusade was launched, and it was by the diversion of that Crusade from its purpose and objective that the conquest and colonization of the Byzantine Empire by the West was realized. A multiplicity of causes and coincidences led up to the event, but the ambition of Venice, which supplied the ships, must rank high among them. A plausible excuse was offered by the cause of restoring Isaac II, whose son Alexius IV had escaped to the West to seek help, and who made lavish promises of reward to his benefactors. But when, in 1203, the Crusaders drove Alexius III out of Constantinople, Isaac II and his son proved incapable either of fulfilling the promises or of stifling the anti-Latin prejudice of their people, who proclaimed an emperor of their own in the person of Alexius V. The Venetians and Crusaders therefore felt justified in taking their own reward by conquering and dividing Constantinople and the Byzantine provinces among themselves. The city fell to them in April 1204. They worked off their resentment against the inhabitants in an unparalleled orgy of looting and destruction, which did irreparable damage to the city and immeasurable harm to East–West understanding.

The Venetians, led by their doge, Enrico Dandolo, gained most from the enterprise by appropriating the principal harbours and islands on the trade routes. The Crusaders set about the conquest of the European and Asiatic provinces. The first Latin emperor, Baldwin I, was the suzerain of the feudal principalities that they established in Thrace, Thessalonica, Athens, and the Morea (Peloponnese). He soon came into conflict with the ruler of Bulgaria. Still more serious was the opposition offered by the three provincial centres of Byzantine resistance. At Trebizond (Trabzon) on the Black Sea, two brothers of the Comnenian family laid claim to the imperial title. In Epirus in northwestern Greece Michael Angelus Ducas, a relative of Alexius III, made his capital at Arta and harassed the Crusader states in Thessaly. The third centre of resistance was based on the city of Nicaea in Anatolia, where Theodore I Lascaris, another relative of Alexius III, was crowned as emperor in 1208 by a patriarch of his own making. Of the three, Nicaea lay nearest to Constantinople, between the Latin Empire and the Seljuq sultanate of Rūm; and its emperors proved worthy of the Byzantine traditions of fighting on two fronts at once and of skillful diplomacy. Theodore Lascaris and his son-in-law John III Vatatzes built up at Nicaea a microcosm of the Byzantine Empire and church in exile. The Latins were thus never able to gain a permanent foothold in Anatolia; and even in Europe their position was constantly threatened by the Byzantine rulers of northern Greece, though in the centre and south of the country their conquests were more lasting.

The most successful of the Latin emperors was Baldwin’s brother, Henry of Flanders, after whose death in 1216 the Latin Empire lost the initiative and the recovery of Constantinople became a foreseeable goal for the Byzantines in exile. The Latin regime was prolonged less by its own vitality than by the inability of the successor states of Epirus and Nicaea to cooperate. In 1224 Theodore Ducas of Epirus, who had extended his territories across the north of Greece and far into Bulgaria, wrested Thessalonica from the Latins and was crowned emperor there in defiance of the Emperor in Nicaea. In 1230, however, he was defeated in battle against the Bulgars before reaching Constantinople; and his defeat gave John III Ducas Vatatzes the chance to extend his own empire into Europe, to ally with the Bulgars, and so to encircle Constantinople. Theodore’s successor was made to renounce his imperial title, and Thessalonica surrendered to the empire of Nicaea in 1246. The Mongol invasion of Anatolia, which had meanwhile thrown the East into confusion, was of great benefit to Nicaea, for it weakened the Seljuq sultanate and isolated the rival empire of Trebizond.

John Vatatzes might well have crowned his achievements by taking Constantinople had he not died in 1254. When his son Theodore II Lascaris (1254–58) died in 1258, leaving an infant son, John IV, the regency and then the throne in Nicaea were taken over by Michael VIII Palaeologus (reigned 1259–82). Michael came from one of the aristocratic families of Nicaea whom Theodore II had mistrusted. But it was he who carried the work of the Lascarid emperors to its logical conclusion. The Byzantine state in Epirus had revived under Michael II Ducas, who set his sights on Thessalonica. Despite several efforts to reach a diplomatic settlement, the issue between the rival contenders had finally to be resolved in battle at Pelagonia in Macedonia in 1259. Michael II was supported by William of Villehardouin, the French prince of the Morea, and by Manfred, the Hohenstaufen king of Sicily. The victory went to the army of Nicaea. Two years later a general of that army entered Constantinople. The last of the Latin emperors, Baldwin II, fled to Italy; and the Venetians were dispossessed of their lucrative commercial centre. In August 1261 Michael VIII was crowned as emperor in Constantinople; the boy heir to the throne of Nicaea, John IV Lascaris, was blinded and imprisoned. In this way, the dynasty of Palaeologus, the last to reign in Constantinople, was inaugurated.

Michael VIII

The new dynasty was thus founded in an atmosphere of dissension, but its founder was determined that it should succeed. He took measures for the rehabilitation, repopulation, and defense of Constantinople. He stimulated a revival of trade by granting privileges to Italian merchants. The Genoese, who had agreed to lend him ships for the recovery of the city from their Venetian rivals, were especially favoured; and soon they had built their own commercial colony at Galata opposite Constantinople, and cornered most of what had long been a Venetian monopoly. Inevitably, this led to a conflict between Genoa and Venice, of which the Byzantines were the main victims. Some territory was taken back from the Latins, notably in the Morea and the Greek islands. But little was added to the imperial revenue; and Michael VIII’s campaigns there and against Epirus and Thessaly ate up the resources that had been accumulated by the emperors at Nicaea.

The dominating influence on Byzantine policy for most of Michael’s reign was the threat of reconquest by the Western powers. Charles of Anjou, the brother of the French king Louis IX, displaced Manfred of Sicily and inherited his title in 1266; he then organized a coalition of all parties interested in reestablishing the Latin empire, posing as the pope’s champion to lead a Crusade against the schismatic Greeks. Michael VIII countered this threat by offering to submit the Church of Constantinople to the see of Rome, thereby inviting the pope’s protection and removing the only moral pretext for a repetition of the Fourth Crusade. The offer to reunite the churches had been made as a diplomatic ploy to previous popes by previous emperors, but never in such compelling circumstances. Pope Gregory X accepted it at its face value, and at the second Council of Lyon in 1274 a Byzantine delegation professed obedience to the Holy See in the name of their emperor. Michael’s policy, sincere or not, was violently opposed by most of his people, and he had to persecute and imprison large numbers of them in order to persuade the papacy that the union of the churches was being implemented. Later popes were not convinced by the pretense. In 1281 Charles I (Charles of Anjou) invaded the empire. His army was beaten back in Albania, but he at once prepared a new invasion by sea, supported by Venice, Serbia, Bulgaria, and the separatist rulers of northern Greece. His plans, however, were wrecked in 1282 by a rebellion in Sicily called the Sicilian Vespers and by the intervention of Peter III of Aragon, which the Byzantines encouraged. Michael VIII died at the end of the same year. He had saved his empire from its most persistent enemy, but he died condemned by his church and people as a heretic and a traitor.

Whatever sins he may have committed in the eyes of the Eastern Orthodox Church, it is true that Michael VIII, by concentrating on the danger from the West, neglected, if he did not betray, the eastern provinces where he had come to power. Frontier defense troops in Anatolia were withdrawn to Europe or neglected, and bands of Turkish raiders, driven westward by the upheaval of the Mongol invasion, began to penetrate into Byzantine territory. Like the Seljuqs in the 11th century, the new arrivals found little organized opposition. Some of the local Byzantines even collaborated with them out of their own antipathy to the Emperor in Constantinople. By about 1280 the Turks were plundering the fertile valleys of western Anatolia, cutting communications between the Greek cities, and their emirs were beginning to carve out small principalities. Michael VIII’s network of diplomacy covered the Mongols of Iran and the Golden Horde in Russia, as well as the Mamlūks of Egypt. But diplomacy was ineffective against Muslim Ghazis (warriors inspired by the ideal of holy war); by the time the threat from Italy was removed in 1282, it was almost too late to save Byzantine Anatolia.

Nor was it possible to raise armies to fight in Europe and Asia simultaneously. The native recruitment fostered by the Comnenian emperors had fallen off since 1261. Estates held in pronoia had become hereditary possessions of their landlords, who ignored or were relieved of the obligation to render military service to the government. The knights of the Fourth Crusade had found many familiar elements of feudalism in the social structure of the Byzantine provinces. By the end of the 13th century the development had gone much further. The officers of the Byzantine army were still mostly drawn from the native aristocracy. But the troops were hired, and the cost of maintaining a large army in Europe, added to the lavish subsidies that Michael VIII paid to his friends and allies, crippled the economy.