Justice League of America, Vol. 1

Finding the Justice League instead of the Justice Society at the latter's headquarters in 1942, the All Star Squadron attack them until Superman explains that they're not only from the future but also a different Earth. Once the situation is explained, the Squadron receive a summons to the White House and President Roosevelt, the League accompanying them. At the White House, the President receives a transmission from Per Degaton using futuristic equipment who threatens all world leaders simultaneously with the nuclear missiles he stole from 1962. In 1982, on Earth-Prime, the Justice Society are attacked by the mutated survivors of the nuclear holocaust. When they find a sole, unmutated survivor, Dr Fate probes his memories and discovers that - following the theft of Russian missiles from Cuba (as shown in part 2 of Crisis On Earth Prime) - nuclear war had broken out. Fate realises that the responsibility for this lay with Degaton. On Earth-Two, in 1942, the heroes of the League and the Squadron attend the test of Degaton's missile and as the mushroom cloud rises over the ocean, a time sphere containing the heroes of the Justice Society appears.