Final answer:
The Abbasid capital city of Baghdad fell to the Mongol forces led by Hulagu Khan in 1258, marking the end of the Abbasid Caliphate's dominance in the region.
Step-by-step explanation:
In 1258, the Abbasid capital city of Baghdad fell to the invading Mongol forces led by Hulagu Khan. This event marked a significant turning point in Middle Eastern history, as it signified the end of the Abbasid Caliphate and the destruction of Baghdad, which at that time was a center of wealth, culture, and trade. The Mongol invasion led by Hulagu Khan devastated the city that had been the seat of Islamic power and learning for five centuries, and the Abbasid Caliphate was unable to recover its former influence after this calamity.