The Legitimacy of Crusades from the viewpoint of Christian Clerics and Its Comparison with the Nature of Muslim's Jihad (holy war) against Crusaders

Crusades are among the longest wars throughout the history which has given historians opportunities to use them as pretext to write about them for two centuries. The reason for these wars, what justification their initiators and wagers had to legitimate these violent wars and what were the nature and principles of Muslim's Jihad against these Christian aggressors in thoughts and views of contemporary jurists are topics which require discussion and reflection.The main hypothesis of the present paper is that Crusades have been the perfect example of holy wars which the new doctrines proposed by Christian clerics on "just war" have not been able to change their nature, because the historical reports about these wars do not allow for their conformity with just war doctrine. Muslim's Jihads against crusaders – whether as preemptive Jihad or as defensive and preventive Jihads–were defensive in nature which contemporary Sunni and Shi’ī jurist consider them as legitimate.