The number of radical Islamist groups fighting in civil wars in Muslim countries has steadily grown over the last twenty years, with such groups outlasting and outperforming more moderate groups. By 2016, Salafi jihadist groups accounted for most of the militant groups in Syria and half of such groups in Somalia. In Iraq, a third of all militant groups were composed of Salafi jihadists. Many analysts argue that the rise of these groups reflects an increase in radical beliefs in Muslim societies. Under certain conditions, however, rebel leaders have strong incentives to embrace an extreme ideology even if they do not believe the ideas that underlie it. When competition is high, information is poor, and institutional constraints are weak, an extremist ideology can help rebel leaders overcome difficult collective-action, principal-agent, and commitment problems. All three of these conditions have been present in the post-2003 civil wars in the Middle East and Africa, and all help explain the emergence and growth of radical groups such as the Islamic State and al-Qaida.

Terrorism is designed to change minds by destroying bodies; it is a form of costly signaling. Terrorists employ five primary strategies of costly signaling: attrition, intimidation, provocation, spoiling, and outbidding. The main targets of persuasion are the enemy and the population that the terrorists hope to represent or control. Terrorists wish to signal that they have the strength and will to impose costs on those who oppose them, and that the enemy and moderate groups on the terrorists' side cannot be trusted and should not be supported. Each strategy works well under certain conditions and poorly under others. State responses to one strategy may be inappropriate for other strategies. In some cases, however, terrorists are pursuing a combination of strategies, and the response must also work well against this combination.