How were the Seljuk Turks involved in the crusades?

The Seljuk Turks played a crucial role in the Crusades by controlling significant territories in the Middle East, including Jerusalem, which prompted Christian powers in Europe to launch military campaigns to reclaim the Holy Land. Their victory at the Battle of Manzikert in 1071 against the Byzantine Empire weakened Byzantine authority and contributed to the call for the First Crusade. The Seljuks engaged in military confrontations with the Crusaders, leading to a series of conflicts that shaped the dynamics of the Crusades throughout the 11th and 12th centuries. Their resistance and the establishment of their own states in the region posed significant challenges to the Crusaders' objectives.