Originally posted by Juntai
He just did it.
That's actually carried over from a 1980s JSA story The Last Days of the Justice Society to remove them from the DCU until they were written back in later where Waverider saved them from that universe.
Last Days of the JSA basically had the Golden Age JSA trapped in a perpetual cycle of Ragnarok. Here's the entire sequence for anyone who's interested:
*This was also the story which revealed that it was merely a "tiny portion" of Spectre's essence that confronted the GEB.
We later learned, in the pages of Sandman, that this 'mini-Ragnarok' was created by DC Odin--and the JSA inadvertently ended up within its endless cycle:
(They were the "further warriors" Odin spoke of.)
During Armageddon: Inferno, Waverider+Spectre freed the JSA from that reality to help fight Abraxis:
It was actually pretty cool how DC tied all of that together.