This is the realm of the Asuras, the jealous gods or titans. These are powerful demigods who are perpetually at war with the gods of the lowest heavens. These are beings devoted to warfare and everything that goes with it; anger, pride, lust for conquest and so forth. Beings in the human realm who manifest these qualities are experiencing Asura-consciousness and are laying the foundation for rebirth here.
There is a Jataka which describes the origin of the war between the gods and the Asuras. (no.31) At one time, it seems, they shared the same realm as the gods of the first heaven. This is located at the summit of the mythological Mt. Sumeru, the world-axis. On the slopes of this mountain there grows a huge tree with intoxicating fruit. The Asuras, being coarser than the devas, were more heavily affected by the fruit and lay about in a drunken stupor.
Sakka, the king of the gods, decided to be rid of these loutish fellows and had them grasped by the heels and tossed down the side of the mountain, to the roots of the tree. Coming to their senses, they realized what they had lost and have been fighting to regain their lost place in heaven ever since.
Generally they get the worst of the battles, because the gods are very hard to kill - they recover quickly from any wound and the only way to finish them off in war is to sever the head. It is indicated in Digha Nikaya 18 that at times when righteousness prevails amongst humans then many more are born into the realms of the devas and the Asura host declines. If this is so, then perhaps the are doing better these days!