Prey to the heavens - John Arcudi

The world's attention is focused painfully on a brutal third-world civil war, a merciless sectarian conflict sparing neither soldier nor civilian, grandmother nor child. But amidst the terror and carnage, where great nations and powerful interests jockey for position and advantage, another blood feud rages in the shadows, one no more humane but decidedly less human. Two warring tribes from the stars have chosen Earth's killing fields as their arena, with each clan sworn to eradicate the other and all who stand between them.