Final answer:
Jerusalem was easily defeated due to its religious significance, attracting military campaigns such as the Crusades, strategic geopolitical positioning, and the tactical skill of Arab soldiers familiar with both Byzantine and Persian military techniques.
Step-by-step explanation:
Jerusalem's vulnerability, leading to its easy defeat, can be attributed to a combination of religious, political, and strategic factors. Over the centuries, it had been the focal point of interfaith harmony and tensions among Jews, Christians, and Muslims.
The Crusades were a manifestation of religious fervour and the military ambitions of European knights, with Urban's directive to liberate Jerusalem motivating many by promising the forgiveness of sins and earthly rewards.
The first Crusaders retook Jerusalem in a horrific slaughter that reflected not just a desire for spiritual redemption but also for territorial control and wealth.
These soldiers were well-versed in Roman and Persian tactics, which they had adopted while serving as mercenaries in the region's conflicts. Additionally, understanding the vulnerabilities of their adversaries, such as the weakened Byzantine and Persian Empires, bolstered Arab military endeavours.
In summary, Jerusalem faced defeats due to its significant religious importance, which attracted military campaigns like the Crusades. Its location at the crossroads of empires made it prone to conquest, while well-trained and strategically adept Arab forces also played a pivotal role in its capture.