The Jerusalem is important to our Muslim group because Jerusalem turned in prayer until Prophet Muhammad changed Mecca and it was taking up to heaven.Even the Muslims are documented in the Quran and the Muhammad give several accounts relating the importance of Jerusalem. It is also the only place in the world of great significance to Muslims.
The reason of the Crusades started is that they arrived in 1095 and it was another invasion similar what they faced in the areas of the empire. The Muslims didn't see it in a holy war. And thats's how the Crusades started.
The effects of the Crusades was the final fatal weakening in the Byzantine Empire and failed to recover Anatolia from the Turks. Even Constantinople was destroyed in 1204. Even some Europeans went on the Crusades and they knew someone they lost.
The Muslim's group view about the Byzantine, Europeans and Jews is that some were superior and some were not. Like for example, the Byzantine were superior because they went to different places and conquered them and maybe the Europeans did that to except the Jews. And that's how the Muslims view them.