Philip E. High 
Sold – For a Spaceship 

They had slept in safety while destruction raged above them. When they awoke and emerged from their places of refuge, the world had changed – totally.For man soon discovered that he was no longer the dominant species on Earth. Now there were other creatures, not only ready to dispute the point but well prepared to prove it.It was later, much later, that the bulk of mankind discovered they had forfeited their birthright, traded their home, the planet Earth – for a spaceship.