Question

Why Did The Crusades Begin?

Answer 1

The first of the Crusades began in 1095, when armies of Christians from Western Europe responded to Pope Urban II’s plea to go to war against Muslim forces in the Holy Land. After the First Crusade achieved its goal with the capture of Jerusalem in 1099, the invading Christians set up several Latin Christian states, even as Muslims in the region vowed to wage holy war (jihad) to regain control over the region.

Answer 2

Long story short the pope called for military support for the Byzantine empire because it had been almost entirely taken under Muslim control, Muslim Seljuk Turks were pillaging their cities, killing and raping there people and conquering the "Holy Land" (Jerusalem) in efforts of retaliation, The Crusade wars began  (The Crusades)