The word jihad is associated with the term struggle, and always refers in some way to the struggle of a Muslim to create a world in better keeping with Islamic precepts. It appears in the Quran, Islam's holy book, and in other authoritative materials to which Muslims refer. There is no consensus among all Muslims about the exact definition of jihad. However, there is wide agreement that:
There are two kinds of jihad: internal, of the self, and external. Jihad can refer to the internal struggle to live one's life in ethical accordance with God's will. It can also refer to the external struggle to defend Islam against unbelievers. This struggle can include war. Some say that internal struggle is the greater jihad; others say that waging war is the greater.
Medieval and modern commentators have examined Quranic verses and the sayings and practices of Muhammad, in order to extrapolate the circumstances that justify jihad as war. Their questions have reflected the different times and places in which they have asked them. Historical questions have included whether jihad is an individual or collective obligation, whether jihad as war can be waged against Islamic rulers, and whether jihad is a defensive war, to be waged when Islamic rule or Islam is under attack.
In the modern world, it has been asked whether jihad can be justifiably waged against Western imperialism in predominantly Islamic areas (Asia and the Middle East), or as part of a national liberation movement.