Why was it difficult for them to capture the city?

Late in the century, Byzantine Emperor Alexius Comenus, also threatened by the Seljuk Turks, appealed to the West for aid. In 1095, Pope Urban II publicly called for a crusade to aid Eastern Christians and recover the holy lands. The response by Western Europeans was immediate.    hope i help :)

Explanation:

muslims have taken his goods and products to different parts of asia an indonesia. sometimes just traveled and trade, but in other occasions, stayed in the place and made a living.

trade was the key for muslims economies to prosper. their commerce routes reached far places like malaysia and java in the 11th century.

another important factor for prosperity was that muslim states served as the middle point for european traders.

they used to travel by land but sailing the seas -the indian ocean- really increase the exportation of products.

quote is the answer your looking for.