Actually, contrary to your claim, bonobos do wage war against each other. They behave very similarly to chimpanzees and humans, as they form coalitions and organize attacks to exterminate rival groups.

It appears that some people prefer to focus on a very specific behavioral trait pinned on bonobos (having sex with group members to diffuse conflicts) just because it fits their preconceived notion of an ideal outcome involving absence of conflicts in general and war in particular. Some people even pin the name "hippie ape" in what looks like a desperate attempt to validate their personal ideals. Yet, bonobos are indeed known for organizing attacks on neighboring primate groups for the express purpose of killing and even eating them.