How did the Battle of Manzikert affect the Byzantine Empire?

The Battle of Manzikert in 1071 was a catastrophic turning point for the Byzantine Empire, marking the beginning of its decline as a militarily viable state. The defeat resulted in the loss of many elite professional troops and the capture of Emperor Romanus IV Diogenes.12

The consequences for the empire were severe:

• Loss of Territory: The defeat opened Anatolia—the heart of the empire’s military and economic strength—to Seljuq Turkish occupation.12
• Political Instability: Following the battle, internal power struggles and civil wars left the eastern frontier undefended, allowing the Turks to advance rapidly toward the capital, Constantinople.2
• Military Vulnerability: The empire’s inability to defend its borders against the Seljuqs and other threats eventually forced Emperor Alexius I Comnenus to seek military aid from Western Europe.32

This appeal for assistance from fellow Christians in the West was a primary catalyst for the First Crusade, as Western leaders viewed the defense of Christendom against the encroaching Muslim power as a holy work.13