The crusaders consolidated their conquests into crusader states. During the 12th and 13th centuries, there were a series of conflicts between those states and the surrounding Islamic states. Appeals from those states to the papacy led to further crusades, such as the Third Crusade, called to try to regain Jerusalem, which had been captured by Saladin (d. 1193) in 1187.[Z] In 1203, the Fourth Crusade was diverted from the Holy Land to Constantinople, and captured the city in 1204, setting up a Latin Empire of Constantinople and greatly weakening the Byzantine Empire. The Byzantines recaptured the city in 1261, but never regained their former strength. By 1291 all the crusader states had been captured or forced from the mainland, although a titular Kingdom of Jerusalem survived on the island of Cyprus for several years afterwards.
Is there an answer to this question (If it cannot be answered, say "unanswerable"): What was the purpose of the Third Crusade?
to regain Jerusalem