Jihad is a concept in Islam that has multiple meanings and interpretations. The word "jihad" literally means "striving" or "doing ones utmost". In its most general meaning, jihad refers to the obligation incumbent on all Muslims, individuals and the community, to follow and realize God’s will: to lead a virtuous life and to extend the Islamic community through preaching, education, example, writing, etc. . There are two basic theological understandings of the word: the "Greater Jihad" is the struggle against the lower self – the struggle to purify one’s heart, do good, avoid evil and make oneself a better person. The "Lesser Jihad" is an outward struggle, which may involve fighting against oppressors and aggressors who commit injustice. Jihad is not "holy war" in the way a crusade would be considered a holy war, and while Islam allows and even encourages proselytizing, it forbids forced conversion. Throughout Islamic history, wars against non-Muslims, even when motivated by political and secular concerns, were termed jihads to grant them religious legitimacy. The concept of jihad has been critical in the history of Islam, and it has been used by resistance, liberation, and terrorist movements alike to legitimate their cause and motivate their followers.