Considerable efforts have been devoted countering violent-extremism in Indonesia. Various empowerment programs and training carried out by the government and the community aims to prevent the spread of radical ideologies. However, extremist groups continue to develop, while traditional extremist groups still in motion, new forms of extremist movements have emerged. Moreover, the impact of violent extremism has increased with the advancement of modern weapons, globalization and information technology such as the Internet and social media. This article pursues to understand the phenomena of people engage in extremists groups and explore arguments to encourage people to commit acts of violence. This article employed literature studies based on excombatants experiences. The article concluded that radicalization and extremism are manifestations of radical systems of thought and belief that develop in people or groups that occurs in several phases of life, not suddenly happening. Several Islamic doctrines such as tawhid, aqeedah, takfir, al wala wal-bara, and jihad, the built an unsatisfactory argument with the existing social and political conditions such as application of kafr and secular system, the hope jihad fi sabilillah, bombing as a form of obligation of jihad as ordered by religion and retaliation for cruelty and oppression of unbelievers against Muslims.