A religious war or holy war (Latin: bellum sacrum) is a war primarily caused or justified by differences in religion. In the modern period, debates are common over the extent to which religious, economic, or ethnic aspects of a conflict predominate in a given war. According to the Encyclopedia of Wars, out of all 1,763 known/recorded historical conflicts, 123, or 6.98%, had religion as their primary cause. Matthew White's The Great Big Book of Horrible Things gives religion as the cause of 11 of the world's 100 deadliest atrocities. In several conflicts including the Israeli–Palestinian conflict, the Syrian civil war, and the wars in Afghanistan and Iraq, religious elements are overtly present but variously described as fundamentalism or religious extremism—depending upon the observer's sympathies. However, studies on these cases often conclude that ethnic animosities drive much of the conflicts.
Some historians argue that what is termed "religious wars" is a largely "Western dichotomy" and a modern invention from the past few centuries, arguing that all wars that are classed as "religious" have secular (economic or political) ramifications. Similar opinions were expressed as early as the 1760s, during the Seven Years' War, widely recognized to be "religious" in motivation, noting that the warring factions were not necessarily split along confessional lines as much as along secular interests.
According to Jeffrey Burton Russell, numerous cases of supposed acts of religious wars such as the Thirty Years' War, the French Wars of Religion, the Sri Lankan Civil War, 9/11 and other terrorist attacks, the Bosnian War, and the Rwandan Civil War were all primarily motivated by social, political, and economic issues rather than religion. For example, in the Thirty Years' War the dominant participant on the "Protestant" side for much of the conflict was France, led by Cardinal Richelieu.
The war of Egyptians with Israelis, Pakistanis versus Hindus, and the conflict between Turkish-origin and Greek-origin Cypriots are recent instances where the ideals of Jihad have been introduced.
[Christianity] Pope Urban II called for the first crusade in 1095. After that, until the Reformation, pope after pope called upon Christian armies to attack Muslim lands. Subsequent popes knew full well that the first crusade had resulted, as the chroniclers said, in the blood of Muslims flowing over the temple mount. Yet for centuries these extremely violent conflicts were initiated by the popes, and indeed imposed as a moral condition on monarchs who faced excommunication if they refused to go.
[Islam] The notion of religious justification for war persists, and threats of Jihad, or holy war, were still heard in the second half of the 20th century. While the influence of the mullah, mufti and other Moslem jurists, theologians and intellectuals is to internalize the Jihad and thus make it a personal struggle to attain moral improvement by self-conquest, the lack of restraint of some popular leaders, militarists, fundamentalists and oil supported politicians in invoking the traditional fourth way appeals to the emotions of the uneducated and threatens peaceful solutions to problems of Islamic and world concern.
Where Shiite Moslems fight Sunni Moslems, as in Lebanon, or in the case of Iran versus Iraq, each faction may also invoke the Jihad tradition, not unlike the clerically-blessed conflicts of Christian Europe. In 1990, Saddam Hussein, as president of Iraq declared a jihad against the forces arrayed against him.
In May 1997 during an interview with CNN, Osama Bin Laden reaffirmed his call for a holy war against Americans. "We have focused our declaration of jihad on the U.S. soldiers inside Arabia. The U.S. government has committed acts that are extremely unjust, hideous and criminal through its support of the Israeli occupation of Palestine." In February 1997 Bin Laden threatened holy war against the U.S. in an interview on the British documentary program, Dispatches. "This war will not only be between the people of the two sacred mosques and the Americans, but it will be between the Islamic world and the Americans and their allies because this war is a new crusade led by America against the Islamic nations."