Justice League of America #207

Direct

As the JLA is about to greet the JSA via the transmatter machine they use to travel between Earth-One and Earth-Two, they're suddenly surprised by the appearance of the Crime Syndicate, who they believed were still in their limbo prison. The JLA then travel to Earth-Two to investigate what happened to their friends. There they find the world was taken over by Per Degaton in 1942. They then travel back in time alongside their JSA allies (freed from the Syndicate's prison) to 1942 where they meet the All-Stars in the JSA's original headquarters.