Gorillas generally try to avoid confrontation in the wild while Chimpanzees often initiate confrontation.
I was watching a show a while back about great apes and almost every single time the silverback male would show himself and beat his chest to an invading group but it was generally done at a fair distance. Usually the invading group would back off.
With chimpanzees they all get involved in getting in each others faces and are pretty quick to go to war.
Remember that incident from a few years ago where a guy and his wife were visiting their former pet chimp at an animal shelter and two other chimps escaped from a nearby cage and tore the couple apart?