From the time of the Muhammad, the founding prophet of Islam, many Muslim states and empires have been involved in warfare. The concept of jihad, the religious duty to struggle, has long been associated with violent struggles with non-Muslims, although many observers refer to such struggle as "the lesser jihad" by comparison with inner spiritual striving. Islamic jurisprudence on war differentiates between illegitimate and legitimate warfare and prescribes proper and improper conduct by combatants. Numerous armed anticolonial military campaigns were waged as jihads.