[dcec2] ^F.u.l.l.~ ~D.o.w.n.l.o.a.d~ T. O. Morrow Kills the Justice League -- Today! (Crisis on Multiple Earths Omnibus, #11) - Gardner F. Fox *PDF% Online

The CRISIS begins here! Before DC's first reboot in 1985, a multiverse existed where each Earth had its own team of superheroes. Earth-1 had the Justice League, Earth-2 had the Justice Society, so on and so forth. Once a year, the boundaries between these worlds would become thin, and the Justice League and Justice Society would team up to fight crime on other Earths!