First Crusade: At the Battle of Civetot, the Seljuk forces of Kilij Arslan destroyed the army of the People's Crusade as it marched toward Nicaea.

The First Crusade (1096–1099) was the first of a series of religious wars, or Crusades, which were initiated, supported and at times directed by the Latin Church in the Middle Ages. Their aim was to return the Holy Land to Christian rule after its conquest by the Rashidun Caliphate in the 7th century. By the 11th century, although Jerusalem had then been ruled by Muslims for hundreds of years, the practices of the Seljuk rulers in the region began to threaten local Christian populations, pilgrimages from the West, and the Byzantine Empire itself. The earliest impetus for the First Crusade came in 1095 when Byzantine emperor Alexios I Komnenos sent ambassadors to the Council of Piacenza to request military support in the empire's conflict with the Seljuk-led Turks. This was followed later in the year by the Council of Clermont, at which Pope Urban II gave a speech supporting the Byzantine request and urging faithful Christians to undertake an armed pilgrimage to Jerusalem.