How did the Crusades add to the Fatimids’ problems in the 12th century?

The arrival of the Crusades in the 12th century significantly exacerbated the decline of the Fatimid dynasty by intensifying the existing pressures on their empire.1

The impact of the Crusades on the Fatimids included:

• Military Conflict: The Crusaders targeted Fatimid-held territories, most notably capturing Jerusalem in 1099 after the Fatimids had occupied the city the previous year. This forced the Fatimids to defend their lands against European forces in addition to ongoing threats from the Byzantines and Seljuq Turks.21
• Political and Religious Isolation: The 12th-century conflict between Islam and Christendom left no room for internal dissension within the Muslim world. As the Fatimids were Shi'i Muslims whose religious doctrine was rejected by the Sunni majority, the pressure of the Crusades indirectly sealed the fate of their Ismāʿīlī theology, which had already been weakened by the Sunni revival.1
• Strategic Vulnerability: The Crusader presence in the region exploited the weakness and division of surrounding Muslim states. This instability ultimately allowed for the rise of new powers, such as the forces under Nūr al-Dīn and his viceroy Saladin, who eventually destroyed the Fatimid Caliphate to unify Egypt and Syria against the Crusaders.3