To many non-Catholics, the Crusades were a violent attempt by popes and European monarchs to destroy peaceful, flourishing Muslim kingdoms in the Middle East and reestablish the reign of Christianity. Many Catholics also buy into this narrative, blushing whenever the Crusades are brought up in conversation.
On the other hand, some Catholics see the Crusades as fully justified attempts to defend Christianity in the Holy Land against invading Muslim armies.
Both versions contain some elements of truth. The Crusades are too complex to be considered fully good or bad. There were Crusaders who were driven by just and unjust motives and each Crusade was different, so they all must be evaluated on their own merits.
Let’s begin with this: Many modern narratives of these expeditions leave out or belittle the reality of Islamic aggression in the early Middle Ages. Since the death of Mohammed in the 7th century, Islam spread rapidly by the sword. Palestine, North Africa, Syria, and many other formerly Christian and Jewish lands quickly fell to the new regime of the Prophet.
Also, while there were periods when conquering Muslim leaders exercised tolerance toward their Jewish and Christian subjects, there were also many periods of persecution. Christians were sometimes enslaved, raped, or subject to higher taxes than their Muslim neighbors. They were pressured to convert to Islam and killed if they refused.