By Matt Krueger and Henry Spangler
Thesis: The Byzantine Empire decline and inevitably collapsed because of outside enemies, economic decay, and weak military.
Over the years that they dominated Western Europe, the Byzantine empire gained many enemies. Their most aggressive enemy, the Seljuk Turks were a growing threat. Towards the end of their empire, the Byzantines were not able to fund as big of an army than in the past, which made them an easy target. The Fourth Crusade saw this and sacked the capital city of Constantinople. The Byzantines never recovered from the attack and eventually the Empire fell to the Turks in 1453 A.D.
The Byzantine empire had relied too much on taxing the peasants. They taxed them very high which helped keep the city wealthy and under control. The empire had been under constant attack which in return people didn't want to invest into buying land which had lost the empire money. Also, once the attacks had stopped the nobles and peasants had started to fight and cause conflict over land, which the peasants originally owned and was the main source of money for the empire.
When at the height of the Byzantine empire in 1025 A.D a strong military seemed less necessary. Therefore, after the death of Basil II which was a strong emperor and was leader at the height of the empire a series of weak and inexperienced emperors replaced him which made the empire weaker. The empire started to rely heavily on foreign mercenaries which created a bigger tax burden on peasants. Also, the Byzantine empire's econcomy weakened so much that they had Italian city-states like Venice and Genoa fight their naval battles for them.