Well not 'cavemen' but specifically neolithic humans. Did they use armies? When did organized warfare start and how organized were the soldiers? What weapons did they have and for what reason would they fight wars?
As a miniature gamer, I am interested in military history. I found this interesting article on the interwebs and thought I'd repost it here. It is a draft of an article by historian Arther Ferrill. It tries to start a discussion about some of this questions. It is a short read and I hope you enjoy it.
Neolithic Warfare by Arther Ferrill