John Barnes: Earth Made of Glass [1999] paperback

At the furthest reaches of the galaxy exist the Thousand Cultures, societies scattered across 31 inhabited worlds in 25 star systems. The Inner Complex – which includes Earth – has been able to exert control over the Thousand Cultures because it contains 90 per cent of all human population and because all traffic must pass through it. But humanity is expanding and the complexes are beginning to fight over access to the frontier worlds. Giraut and Margaret are posted to the frontline – Quidde, base of Chaka Home: a culture based on a Millennialist black American sect claiming spiritual descent from Chaka Zulu’s army. But they aren’t the only culture on Quidde and history looks very much like repeating itself as three factions engage in a struggle that echoes the bloody twentieth century wars in Rwanda and Bosnia. Giraut and Margaret must hunt out the last vestiges of good in a corrupt world – or risk seeing humanity as we know it disappear forever.