Could you give a little info on the Earth 2 storyline/characters (or at least how it starts out, I'm not sure what the current issue # is)? I personally know little to nothing of it, I'd appreciate a minor summary. Put it in spoiler tags if you want.
Basically Earth 2 was similar in a lot of ways to Earth One with some minor differences here and there.
In the Justice League comic the opening fight that brings them together is a fight against an invasion from Apokalips, not that they know it at the time, some portals open up and there are some Parademons etc.
In Earth 2 this assault was a thousand times worse, and in a last-ditch effort to save their earth, three of their greatest Wonders (their word for heroes, as their Justice League were known as the 8 Wonders of the World) gave their lives to save it. Those three Wonders were Superman, Batman and Wonder Woman. The casualties on Earth were massive, leaving giant Apokolips fire-pits marring the surface of Earth (it's explained in Issue #0 how this happened). Of the 8 Wonders, 3 were killed, two were missing in action (their adventure continue in World's Finest) and it is unknown what remains of some of the others.
After this, many countries united to form the World Army, to ensure nothing like this could ever happen again. In a world now without Wonders, with No Hal Jordan and Green Lantern Corps, No Justice League, No Batman or Wonder Woman or Superman etc.
This is basically how the story starts, you are about to meet a new age of heroes, not like the ones you know. Earth 2 is basically the New 52 to answer to the Justice Society of America, WWII Era heroes like the original Flash and Green Lantern, except now they are now in a modern setting in a different kind of "World War".
TL;DR: It's a world where Batman, Superman, Wonder Woman, Robin, Supergirl and nearly all the characters from Earth 1 don't exist, but different versions of the Flash & Green Lantern do who got their powers in different ways.
