The great series of western holy wars were the Crusades, which lasted from 1095 until 1291 CE. The aim was to capture the sacred places in the Holy Land from the Muslims who lived there, so it was intended as a war to right wrongs done against Christianity.
The first Crusade was started by Pope Urban II in 1095. He raged at the capture of the holy places and the treatment given to Christians, and ordered a war to restore Christianity. He said that the war would have the support of God:
"Let this be your war-cry in combats, because this word is given to you by God. When an armed attack is made upon the enemy, let this one cry be raised by all the soldiers of God: It is the will of God! It is the will of God!"
"...Whoever shall determine upon this holy pilgrimage and shall make his vow to God to that effect and shall offer himself to Him as a living sacrifice, holy, acceptable unto God, shall wear the sign of the cross of the Lord on his forehead or on his breast."
The pope also absolved all who took part in the crusade of all their sins.
The first Crusade captured Jerusalem after bitter fighting, and the residents of the city were brutalised and slaughtered by the Christian invaders. The invaders' conduct breached the principles of modern just war ethics, and the massacres still colour Islamic politics today.
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funny how the roman catholic church is one of the richest organizations in the world now
