The Seljuk Turks were a Muslim empire that ruled over much of Asia Minor and were ruled by a Sultan. When the Seljuks took the Holy Land it sparked the crusades.
The Third Crusade (1189-1192) and Richard the Loinheart
The first crusade, headed by four noblemen led 30,000 crusaders through Anatolia in hopes of reclaiming the Holy Land from the Muslim forces. It ended in success, capturing many cities including Antioch and in 1099 Jerusalem fell resulting in four new crusader kingdoms.
The Children's Crusade (1212)
At the beginning of the second crusade the crusaders won early battles due to the disunity of Muslim forces. Eventually the new Muslim empires created by the newly dissipated Seljuk empire banded together to beat back the crusaders at Damascus.
The Later Crusades
The third crusade started when Salah al-Din's Muslim forces took back some of the Holy Land, including Jerusalem, controlled by crusaders. Led by Richard the First, the crusaders took back Acre. During a prisoner exchange Richard killed many of his prisoners before trading them for crusader prisoners . The crusade fizzled out after Richard could not retake Jerusalem
The crusaders take Acre
The Children's Crusade was a movement by the poor rather than the Military. Most "soldiers" never made it to the Holy Land, instead they were probably sold into slavery.
The later crusades were a jumble of underfunded and under planned events that, if anything, quickened the loss of crusader land. In 1291 the Muslim troops took the crusader's last city, Acre.