Starswarm by Brian Wilson Aldiss

"One million years have passed since ancient man first launched his frail metal crafts into the great darkness named "outer space." Now, distant galactic clusters are home to the myriad descendants of the inhabitants of Old Earth. Now, each world, light years separate from the others, forms part of an island universe called "Starswarm." Yet each island remains uneasily bound to all others, for the creatures that people Starswarm were once of the race called Human, and among these 10,000 brave new worlds, man's brutal, timeless struggle for conquest still goes on ..."--Back cover