The era from about 1025 to 1453 witnessed the decline of the Byzantine Empire and its ultimate destruction. Loss of territory, internal discord, and defeats by the crusaders were blows from which the empire could not recover. There were new enemies in this era—the Petcheneg and Seljuk Turks to the east and north, and the Normans and Slavs to the west.
There was the free peasantry upon which the government depended for taxes and recruits. When the empire had been under constant attack, land had been a poor investment. But once stability started to return in the eighth century, many nobles looked greedily upon the farmlands controlled by the free peasantry. There was a constant battle as the nobles tried to get these lands and enserf the peasants.
The Byzantine empire had survived many Germanic and Hunnic tribal raids and migrations in the 5th and 6th centuries, but could not recover, hold, and govern the entire Mediterranean world. Constantinople itself weathered major Arab sieges in the 620's.
The Arab invasions occurring in the 6th and 7th centuries declined city life and commerce in most of the empire except Thessalonika and Constantinople. Warfare inhibited agriculture and education, and the empire could no longer maintain the complexity of the late Roman empire; yet, it managed to endure and adapt for a while longer.
The role of the Byzantine Empire was central to the crusading period. Byzantium, along with Latin Christendom and Islam, were the three dominant civilizations of the Middle Ages. It was primarily these three societies that clashed during the crusades, which may have hastened the decline of the Byzantine Empire.
The 12th century was marked by a series of wars against the Hungarianss and the Serbs. Emperor Manuel Comnenus campaigned successfully in this region, forcing the rebellious Serbs to vassalage (1150-1152) and leading his troops into Hungary.
After the death of Comnenus the Byzantine Empire fell into permanent decline. The poor leaders that followed lost all of the gains that were obtained over the past hundred years. Then, as a result of an unwise taxation increase, a Bulgarian rebellion was organized in 1180, and one year later the lands were lost. These events greatly contributed to the empire's decline.
During the 14th century, the Ottomans Turks invaded the Balkans and Asia Minor. Constantinople finally felt under the rule of the Ottoman Empire, which marked the end of the Byzantine period.