A religious war or a war of religion, sometimes also known as a holy war, is a war which is primarily caused or justified by differences in religion and beliefs. In the modern period, there are frequent debates over the extent to which religious, economic, ethnic or other aspects of a conflict are predominant in a given war. The degree to which a war may be considered religious depends on many underlying questions, such as the definition of religion, the definition of 'religious war', and the applicability of religion to war as opposed to other possible factors. Answers to these questions heavily influence conclusions on how prevalent religious wars have been as opposed to other types of wars.
A sample scene of the Taiping Rebellion.
Saladin and Guy of Lusignan after the Battle of Hattin of 1187
The St. Bartholomew's Day massacre of French Protestants, 1572
Midianite women, children and livestock taken captive by Israelite soldiers after all Midianite men had been killed and their towns burnt. Watercolour by James Tissot (c. 1900) illustrating the War against the Midianites as narrated in Numbers 31.
Religious fanaticism, or religious extremism, is a pejorative designation used to indicate uncritical zeal or obsessive enthusiasm that is related to one's own, or one's group's, devotion to a religion – a form of human fanaticism that could otherwise be expressed in one's other involvements and participation, including employment, role, and partisan affinities. Historically, the term was applied in Christian antiquity to denigrate non-Christian religions, and subsequently acquired its current usage with the Age of Enlightenment.
Members of the Jansenist sect having convulsions and spasms as a result of religious fanaticism. Engraving by Bernard Picart.
Osama bin Laden and Ayman al-Zawahiri of al-Qaeda have promoted the overthrow of secular governments.