3 villains each from Earth-1 and Earth-2 hatch a plot to commit crimes, then hide out on the other Earth. To ensure their success, the villains of Earth-1 mystically trap the Justice League of America in their headquarters. But the Justice League of America summons the Justice Society of America and switches places with them.
More Details...Justice League of America #21 GD+ "Crisis on Earth" part 1. First meeting of the Justice Society of America and the Justice League of America. First meeting of Green Arrow and Black Canary. 1st appearance of Dr. Fate and Hourman in the Silver Age. 2nd appearance of Chronos.
3 villains each from Earth-1 and Earth-2 hatch a plot to commit crimes, then hide out on the other Earth. To ensure their success, the villains of Earth-1 mystically trap the Justice League of America in their headquarters. But the Justice League of America summons the Justice Society of America and switches places with them.