"Slay the unbelievers wherever you find them . . ." (Sura 9:5).
The Islamic idea of jihad, which is derived from the Arabic root meaning "to strive" or "to make an effort," connotes a wide range of meanings, from an inward spiritual struggle to attain perfect faith to an outward material struggle to promote justice and the Islamic social system. The former meaning was emphasized by Sufis (Muslim mystics), who popularized a tradition describing the inner jihad as greater than the outer jihad. When used in the latter sense, jihad is closely identified with the injunction in the Qur'an, the revelation of God to the prophet Muhammad, to the Muslim community to "command the right and forbid the wrong" (3:104, 110). The close connection of jihad with the struggle for justice is reinforced in the hadith, the sayings and actions attributed to Muhammad. One of the best known states that a Muslim must strive to avert injustice first by actions, and if that is not possible, by words, and if that is not possible, at least by intentions.
During the period of Qur'anic revelation while Muhammad was in Mecca (610-622), jihad meant essentially a nonviolent struggle to spread Islam. Following his move from Mecca to Medina in 622, and the establishment of an Islamic state, fighting in self-defense was sanctioned by the Qur'an (22:39). The Qur'an began referring increasingly to qital (fighting or warfare) as one form of jihad. Two of the last verses on this topic (9:5, 29) suggest a war of conquest or conversion against all unbelievers.