Definition:
The need for vengeance has been posited as a key, if not the key, emotion that motivates terrorists.
In 1981, Dr. Martha Crenshaw, an expert on political terrorism, writing on terrorism's causes, suggested that:
If there is a single common emotion that drives the individual to become a terrorist, it is vengeance on behalf of comrades or even the constituency the terrorist aspires to represent. (At the same time, the demand for retribution serves as public justification or excuse.) A regime thus encourages terrorism when it creates martyrs to be avenged. Anger at what is perceived as unjust persecution inspires demands for revenge, and as the regime responds to terrorism with greater force, violence escalates out of control.
From, "The Causes of Terrorism," Comparative Politics, July 1981.