The open insurgency stage, the final phase, according to the CIA’s report, is characterized by sustained violence as increasingly active extremists launch attacks that involve terrorism and guerrilla warfare, including assassinations and ambushes, as well as hit-and-run raids on police and military units. These groups also tend to use more sophisticated weapons, such as improvised explosive devices, and begin to attack vital infrastructure (such as hospitals, bridges, and schools), rather than just individuals.
