IIUC, YHWH started out as either a storm god or a sun god. Some of the evidence seems to indicate sun god, but, e.g., clouds as the chariot of god seem to indicate storm god. Also he sometimes acts at night. War god would just be a secondary characteristic.
And again, IIUC, the really early ancestors of the Jews were a small tribe with one god. Calling them monotheists isn't quite right, though, because they didn't deny the existence of the other gods, they just said they're not our god. The problem here is that when fleeing Egypt they took along a whole bunch of other folk, who followed other gods. That is the period were they started changing into "our god is the only real god", but also the period where they needed to merge the gods together into one god. Please note that the Mosaic commandments don't deny the existence of other gods, they just claim you should only worship this god that gave me these commandments, but about which I'm not going to tell you anything explicit. So no images allowed, and you can't say his name, or even write it in a way that would let someone else say it. (I've always liked the suggestion that it was "Yahu! Wahu!".) But I'm rather convinced, without other evidence, that the purpose of this was to allow various different creeds to be merged into one.