A religious war is a war caused by or justified religion. As religion has been very important in many societies, especially before recent secularization in some areas, stating religious causes or justifications for wars have been very common.
Wars between different tribes, peoples, cities, and countries have often involved different religions. Examples include the many wars described in the Jewish Bible, often described as religiously motivated. Other examples include the Crusades and Islamic Jihadist and expansionist wars. There are also many wars stated to be motivated by religious difference within the same religion.
Critics of stated religious influences on wars may to varying degree dispute the importance of religion and argue that stated religious justifications are concealing other causes. Marxists and other influenced by Marxism may see socioeconomic factors as the main force behind historical developments. Another view is that some religious wars are influenced by ethnic/racial conflicts or that religious wars have been important in history because they are similar to ethnic/racial conflicts, for which there may be genetic instincts involved, such as regarding racial genetic interests.