Droma: Book 1 Kerma

Following a worldwide cataclysm a few centuries earlier the isolated and remote island of Droma has had no contact with other peoples except a little desultory trade with the country of Valkil ('it's a very long way away to the south and west, at least two weeks by ship'). The people have lived a hard life, not much above subsistence level for generations, but completely without conflict and have acknowledged no enemy except the weather. One day in summer an army from Valkil invades, intent...