2.31 Why were there violent Crusades?

Muslims, barbarians, and the Orthodox

The original idea behind the Crusades was to protect Christians in the Holy Land and pilgrims on their way to holy places against violence and oppression by Muslims.

However, the Crusaders sometimes used too much violence. Often, destruction and pillaging occurred under the guise of a Crusade. There can be no justification for such things! In 2001, Pope John Paul II said: “For all those times Muslims and Christians offended each other, we must ask forgiveness of God and we must forgive each other.”

The Crusades were intended to protect Christians in the Holy Land against oppression by Muslims, but crusaders often used the wrong means.
This is what the Popes say

The God whom we seek to serve is a God of peace. His holy Name must never be used to justify hatred and violence… All too often, young people are being radicalized in the name of religion to sow discord and fear, and to tear at the very fabric of our societies. How important it is that we be seen as prophets of peace, peacemakers who invite others to live in peace, harmony and mutual respect! May the Almighty touch the hearts of those who engage in this violence, and grant his peace to our families and communities. [Pope Francis, Ecumenical and interreligious meeting in Nairobi, 26 Nov. 2015]