The original "Buck Rogers" story -- Nowlan’s novella tells about America in the 25th century, conquered by Hans in 2109 A.D. and only now beginning to rebel. The Hans are invaders from Asia with highly advanced technology. They have great aircraft armed with disintegrator rays that turn whatever they hit into nothing. From time to time, they raid American land "to keep the 'wild' Americans on the run within the shelter of their forests, and prevent their becoming a menace to the Han civilization." (Summary from Wikipedia).