The Silver Age Flash enemies all lived on Earth-One and started out as enemies of the second Flash, Barry Allen, as well as the third Flash, Wally West, and the fourth, Bart Allen, after the death of Barry Allen.
Enemies of the Silver Age Flash resided on Earth-One and began their conflict with the second Flash, Barry Allen, also facing the third Flash, Wally West, and the fourth, Bart Allen, after Barry Allen's demise.