After an introductory chapter, in which the studies of previous scholars are examined, warfare in the Latin East in the period is placed in its historical context. It involved not only crusades: there were long periods of truce when warfare was restricted to raiding expeditions, while many conflicts took place between Christians themselves. The Latin armies are then considered. There were many elements in them - the feudal levy, the Military Orders, mercenaries and other paid troops, confraternities and crusaders - but the armies proved consistently inadequate to deal with the Muslim threat to the Latin East, The Christians, therefore, were dependent on castles and fortified towns for their survival, and it was essential that these should be adequately built, maintained and garrisoned. The Military Orders took increasing responsibility for them during the thirteenth century. Strongpoints had a number of functions, both defensive and aggressive, but lack of manpower meant that their role was often restricted. In the thesis there follows a consideration of the forms armed conflict took. Battles were not a prime factor in the decline of the Latin East, because the Franks were rarely able to raise an army to fight in the open with the Muslims. Battles therefore tended to take place during crusade expeditions, when adequate numbers were available. On some occasions - the First Crusade of Louis IX, and Theobald of Champagne's Crusade, for example - a lost battle seriously impaired a campaign. Battles should be distinguished from raids. The Muslims used raiding expeditions as an integrated part of their efforts to remove the Franks from the east. But the raid was used as an end in itself by the Franks and towards the end of this period it had become their principal means of carrying war to their enemies. Finally, there is a study of sieges. The capture of strongpoints by the Muslims, particularly in the second-half of the thirteenth century, progressively loosened the Franks' grip on the area. Sieges undertaken by the Franks often became matters of attrition, whereas when they were defending themselves, a Muslim assault often proved decisive in a short space of time. The Franks' lack of manpower was again significant.