Decline was a process, not an event
The capture of Constantinople in 1453 is the date everyone remembers, but by then the empire had been shrinking for centuries. Historians disagree about when decline began and which causes mattered most, and they caution against hindsight: at several points a recovery looked possible. A useful way to follow the story is to treat it as a series of shocks, each of which left the state a bit smaller and poorer than before.
Warning signs after Basil II
Basil II died in 1025, leaving a large and wealthy empire. Within a generation, the signs of strain were visible. His successors were often weak, and rivalry between military families and civil officials made policy unsteady. Over time the army was neglected in some periods and partly replaced with paid foreign troops, including mercenaries. At the same time new enemies appeared: Normans in southern Italy, Pechenegs on the Danube frontier and Seljuk Turks in the east.
Manzikert and its aftermath
In 1071 Emperor Romanos IV Diogenes was defeated and captured by the Seljuk sultan at Manzikert in eastern Anatolia. The Battle of Manzikert did not end the empire. The sultan treated the emperor with respect and released him, and the empire lost little territory in the battle itself. The real damage came afterward: civil wars broke out in Constantinople, armies marched against each other rather than against the Turks, and Turkish groups moved into the interior of Anatolia, which had been the empire’s richest recruiting ground. Historians still debate whether Manzikert deserves its fame or whether the civil wars were the greater cause.
The Komnenian revival
Emperor Alexios I Komnenos took the throne in 1081 and began to stabilize the state. With help from the first crusade, in which Western armies passed through his lands in 1096-1097, he recovered coastal Anatolia. His successors, notably John II and Manuel I, campaigned in Syria, the Balkans and Italy. This was a real recovery, though it depended on a more personal and family-based style of government. After Manuel suffered a major defeat by the Turks at Myriokephalon in 1176, the revival faded. His death in 1180 was followed by a period of intrigue and short reigns.
1204
The turning point many historians stress is the Fourth Crusade. A crusading army, short of money and in debt to Venice for ships, was diverted to Constantinople in support of a claimant to the throne. When the promised payments failed to arrive, the crusaders and Venetians took the city by assault in April 1204 and sacked it. Churches, palaces and libraries were plundered, and relics and artworks were carried west, some to Venice.
The empire broke apart. A Latin Empire was set up in Constantinople, with Venetian influence over trade and territory. Greek successor states formed in exile, the most important being the Empire of Nicaea, along with Epirus and Trebizond. For the rest of the Byzantine story, the city was recovered, but the damage was lasting: the treasury, the defense of the provinces and the unity of the Greek world were all weakened.
The restoration of 1261 and its limits
Michael VIII Palaiologos, ruler of Nicaea, took Constantinople back in 1261, helped by the Latin regime’s weakness and by Genoese support. The restored empire was a much smaller state. It had to face several enemies at once: Charles of Anjou in the West, Serbia and Bulgaria in the Balkans, and growing Turkish emirates in Anatolia.
The 1300s brought more trouble:
- repeated civil wars between rival claimants, in which each side sometimes hired Turkish or Serbian allies
- the Black Death, which reached Constantinople in the late 1340s and reduced the population
- the rise of the Serbian kingdom, which for a time took much of Macedonia and northern Greece
- the Ottoman advance, which captured Bursa in 1326 and Nicaea in 1331, and crossed into Europe in the 1350s
Italian merchants controlled much of the empire’s commerce, leaving the government with little revenue. The emperor increasingly depended on loans, pawned valuables and foreign help.
The Ottoman squeeze
By the late 1300s the Ottomans surrounded Constantinople on land. The emperors became vassals of the sultan, paying tribute and sometimes supplying troops. The Ottomans defeated Balkan allies at Kosovo in 1389 and a crusader army at Nicopolis in 1396. A brief reprieve came in 1402, when Timur defeated the Ottoman sultan Bayezid I near Ankara and plunged the Ottoman state into civil war. The empire regained some territory, including Thessalonica for a time, but could not turn the pause into lasting strength.
Emperor John VIII went to Italy to seek aid in the 1430s, and at Florence in 1439 an agreement on church union was signed. It was rejected by many in Constantinople and brought little help. A crusading force was defeated at Varna in 1444.
The last years
By the 1440s the empire consisted of Constantinople, some nearby areas and the Morea, a Greek territory in the southern Peloponnese. The last emperor, Constantine XI, took the throne in 1449. The city fell to Mehmed II in 1453, and the Morea and Trebizond fell to the Ottomans in 1460 and 1461.
Why did it fall?
Most historians would point to a combination of factors rather than one cause: loss of land and revenue, internal conflict, the damage of 1204, the pressure of stronger neighbors and the economic power of Italian cities. The empire’s flexibility had kept it alive through many crises, but by 1453 there was little left to reorganize.