suspended animation
Armageddon 2419 A.D. and The Airlords of Han by Philip Francis Nowlan
These are the original Buck Rogers novels. Caught in a mining accident in 1927, Anthony “Tony” (Buck) Rogers fell into a state of suspended animation and only came back to consciousness 492 years later. He awakens in a world where Americans are mere back woods gangs “not worth the trouble of subduing” by the ruling Han Airlords. And so the stage is set for the “Second War of Independence.”