Military history of the Crusader states
The Seljuk–Crusader War began when the First Crusade wrested territory from the Seljuk Turks during the Siege of Nicaea in 1097 and lasted until 1128 when Zengi became atabeg of Aleppo. At the latter date, the chief threat to the Crusaders from the east and north became the Zengids. The conflict was generally fought between European Crusaders and the Seljuk Turks and their vassals. The Muslim Syrian emirates occasionally allied themselves with the Christians against rival states.
Crusades
As the Ottomans pressed westward, Sultan Murad II destroyed the last Papal-funded Crusade at Varna on the Black Sea in 1444 and four years later crushed the last Hungarian expedition. In 1453 they extinguished most of the remains of the Byzantine Empire with the capture of Constantinople. John Hunyadi and Giovanni da Capistrano organised a 1456 Crusade to oppose the Ottoman Empire and lift its Siege of Belgrade. Æneas Sylvius and John of Capistrano preached the Crusade, the princes of the Holy Roman Empire in the Diets of Ratisbon and Frankfurt promised assistance, and a league was formed between Venice, Florence, and Milan, but nothing eventually came of it. In April 1487 Pope Innocent VIII called for a Crusade against the Waldensians of Savoy, the Piedmont, and the Dauphiné in southern France and northern Italy because they were unorthodox and heretical. The only efforts undertaken were in the Dauphiné, resulting in little change. Venice was the only polity to continue to pose a significant threat to the Ottomans in the Mediterranean, but it pursued the "Crusade" mostly for its commercial interests, leading to the protracted Ottoman–Venetian Wars, which continued, with interruptions, until 1718. The end of the Crusading in terms of at least nominal efforts by Catholic Europe against Muslim incursion, came in the 16thcentury, when the Franco-Imperial wars assumed continental proportions. Francis I of France sought allies from all quarters, including from German Protestant princes and Muslims. Amongst these, he entered into one of the capitulations of the Ottoman Empire with Suleiman the Magnificent while making common cause with Hayreddin Barbarossa and a number of the Sultan's North African vassals.