Rampage is an active ability exclusive to the Simian Flu DLC. It allows the player to save apes from human captivity, which leads to the destroying of Gen-Sys labs if present. Apes will prioritize attacking these labs and once it is destroyed, the rampage ends automatically.
This ability can be used in any country where there are intelligent apes, even without a Gen-Sys lab present. This often results in mass casualties, however.