Chimps in the wild (in West Africa) have been seen making spears and using them to kill prey. Per the article:
"The tools (spears) are made from living tree branches that are detached and then modified by removing all the side branches and leaves, as well as the flimsy terminal end of the branch," lead author Jill Pruetz told Discovery News. "Some individuals further trim the tip of the tool with their teeth," added Pruetz, who is a professor in the Department of Anthropology at Iowa State University. "They average about 75 centimeters (around 30 inches) in length."....Spear in hand, the chimps would sneak up on bushbabies -- small, big-eyed primates -- and stab them to death. Bushbabies, which are nocturnal and are also called "galagos," spend much of their days snoozing in tree cavities. They can become an easy filling meal for a spear-wielding chimp.
We should follow them, and see how long it takes to turn into an arms race between chimp tribes. Jane Goodall obeserved a mother and daughter chimps kill another female chimp, so they do know how to kill each other.
It is not only chimps that will kill each other. There are many species of animals in which the members will kill each other if the circumstances are dire enough. Needless to say that humans are no exception.
I was more into the arms race angle of it. The other animals don't use weapons. Right now, it sounds like they are using their spears to stab with, much like a knife. How long will it take to learn to throw them at each other in a fight?. And then when they throw them, they will learn that the longer it is, the easier it is to aim them, etc.etc. etc....