Not mentioned is the fact that the Crusades were for the purpose of freeing the huge numbers of Christians taken captive by the Muslims (including many Europeans kidnapped from the Mediterranean) and expelling the Muslims from the Christian holy sites, which they had overrun and captured.
The Crusades were not just for the heck of it, but because Islam was pushing at the borders of Europe too and the popes had given many warnings and asked for help many times from the European rulers (who were too busy fighting among themselves to have the strength or resources to fight the real threat).
The Crusades were essentially defensive. The final crusade ended in disaster, mostly because by then many of the soldiers were mercenaries, engaged in looting, and also went on a rampage when the Greeks (who had agreed to fund them) refused to pay up. While there were differences between the Eastern and Western church authorities at the time, the famous attack by the Crusaders was actually a pay dispute. So while the Crusades declined in religious or even military value over time, they were originally defensive actions.
Correct me if I’m wrong. In the first crusade there were no Muslims. They were pagans. It was Mohamed who noticed that the Christians, unified by their religion, could fight side by side even though some did not have a common language, who started Islam. Islam was intended to be 180 degree counter to Christianity. It unified the pagans and granted its new members special privileges in loot and slaves that were not enjoyed by non-members.
Where Christianity held wider aspirations Islam’s only purpose, originally, was to destroy Christianity. Where Christianity was one component of a wider society, Islam was intended to supplant all components and become law, government, education and creed all in one.