In the parallel world first introduced in S. M. Stirling’s The Sky People, aliens terraformed Mars (and Venus) two hundred million years ago, seeding them with life-forms from Earth. Humans didn’t suspect this until the twentieth century, but when the first probes landed on our sister worlds, and found life—intelligent life, at that—things changed with a vengeance. By the year 2000, America, Russia, and the other great powers of Earth are all contending for influence and power amid the newly-discovered inhabitants of our sister planets. Venus is a primitive world. But on Mars, early hominids evolved civilization earlier than their earthly cousins, driven by the needs of a harsh world growing still harsher as the initial terraforming runs down.
