A20th-century territorial conflict caused by religious differences was fought between

Orthodox Catholic and Muslims

Religious identity not only survives but can take on heightened significance when national and political alliances break apart, as happened in the former Yugoslavia in the early 1990s, when Serbs, Croats and Bosniacs were divided along Orthodox, Catholic and Muslim fault lines.

The Qur'an recognises the human propensity for conflict and gives permission for defensive warfare. Muslim scholars developed a just-war theory although admittedly in the ensuing centuries jihad was also used to further the territorial ambitions of ruthless leaders, just as today it's distorted to justify terrorist bombings.

Require the nobles and clergy to pay taxes.