Michael Moorcock 
Wrecks of Time 

Earth zero to Earth fifteen – which was the real one?What the inhabitants of Greater America didn’t realize was that theirs was the only inhabited landmass, apart from one island in the Philippines. They still talked about foreign countries, though they would forget little by little, but the countries were only in their imaginations, mysterious and romantic places where nobody actually went..That was the way it was on E-3, one of the fifteen alternate Earths that had been discovered through the subspace experiments.Professor Faustaff knew that these alternate earths were somehow recent creations, and that they were under attack from the strange eroding raids of the mysterious bands known as the D-Squads. But there were tens of millions of people on those Earths who were entitled to life and protection-and unless Faustaff and his men could crack the mystery of these worlds’ creation and the more urgent problem of their impending destruction, it would mean not only the end of these parallel planets, but just possibly the blanking out of all civilization in the universe.