Every Justice League you can think of from across the DC multiverse comes to fight the Justice-Doom War.
I feel like gathering Justice Leagues from throughout time and the multiverse (including the Justice Society) for a fight against the Legion of Doom across three separate time periods should be a bigger deal than it is. I Also feel like it should be called a Crisis - I don’t make the rules, I just endlessly nitpick about them, friends - but that’s neither here nor there.
But really, think about it: until Justice-Doom War, the last we’d heard of the Justice Society was when Jay Garrick flashed (pun unintentional but gladly accepted) across the page in The Button, sixty-some issues ago in Batman and The Flash. Otherwise he and many others from that team were in the good but not Jsa book Earth 2: Society.