From the 1960s through the 1980s, one of the most enjoyable traditions carried on by DC Comics was the annual crossover between the Justice League of America on Earth-1 and the Justice Society of America on Earth-2, with half of the fun being derived from how the JLA writers would up the ante from year to year. Over the course of the various crossovers, the JLA and the JSA found themselves working with the Freedom Fighters, the Seven Soldiers of Victory, the Legion of Super-Heroes, the New Gods, the heroes of Earth-S (home to the Shazam! family and their ilk, don't you know), and a variety of time-tossed heroes ranging from the Viking Prince to Jonah Hex.
The last big JLA-JSA throwdown, however, spanned time and space (not to mention Justice League of America #207-209 and All-Star Squadron #14-15), taking them to a variety of worlds and eras, the most notable involving a trip to Earth-2 during World War II, where members of the JLA and the JSA from the present teamed up with Earth-2's premier wartime supergroup, the All-Star Squadron. (We don't use an acronym for that one, for reasons which will become clear as soon as you try it yourself.) During the course of their trip, the heroes found their way to the White House, where they met President Franklin Delano Roosevelt. As befits a man with his reputation, FDR didn't so much as blink an eye when presented with heroes from another world and another time.