If they can, male chimpanzees try to kill the male members of neighboring groups. Males work together when they spot a chance to make a lightning raid on an isolated male from the other group. They kill him. In Gombe, Tanzania, a group in the 1970s was seen to kill seven of their neighbors one by one, until all were gone. It can take years for this to happen but, when it does, the remaining females and the neighboring territory are added to the now larger group. Attacks like this are carefully planned, done only when success is likely, and carried out in silence.