The development of Earth-Two largely mirrors that of Earth-One. It is divergent from the main Earth in the period of time in which the heroes developed and operate, most of them originated in or around World War II. Its heroes experienced more or less parallel development with their Earth-One counterparts, with some exceptions. The heroes on Earth-Two occasionally interacted with those on Earth-One.
Though Earth-Two bears much resemblance to the Earth-One universe, it does have some notable differences from Earth-One. The most prominent is the Earth's timeline, which is shifted back somewhat so that major events, such as the emergence of masked heroes and the explosion of Krypton, take place earlier in the chronology. Earth-Two received much of the magic that had been shunted out of Earth-One, resulting in magical dominance over science in Earth-Two.
Politically, Quebec is a separate nation from Canada; South Africa abolished apartheid earlier, in keeping with the shifted timeline; and Atlantis was raised from the sea and parts of it are ruled by a queen; as a result of being on the surface, Atlanteans have no underwater adaptations. The Legion of Super-Heroes does not exist in Earth-Two's future. The Justice Society of America and All-Star Squadron both are formed by Franklin Delano Roosevelt. Earth-Two was destroyed during the Crisis on Infinite Earths.
Earth-Two was created by Gardner Fox and Carmine Infantino.
Golden Age / Earth-Two
Since Earth-Two is essentially parallel to Earth-One, it is home to many Golden Age counterparts of Earth-One heroes, including Kal-L, the counterpart of Superman; Princess Diana Trevor, the counterpart of Wonder Woman; Jay Garrick, the counterpart of Barry Allen; and Alan Scott, the counterpart of the Green Lanterns. Heroes native to Earth-Two who share no Earth-One counterpart, or who immigrated to Earth-One and became heroes there include Johnny Quick, Power Girl and the Sandman.
Post-52 Weeks / Earth-Two
A new Earth-Two was created in the aftermath of 52. This Earth is not the same as the original Earth-Two, and is home to the Justice Society Infinity, an amalgamation of the Justice Society of America and Infinity, Inc. This Earth-Two is visited by Power Girl, who initially believes it to be her native Earth, but is later proven incorrect.
The New 52 / Earth-2
Following the New 52 reboot, the Earth-2 concept was rebooted. For this new concept for Earth-2, the center point is the invasion of Earth by Apokolips (led by Steppenwolf). Like the mainstream DC, the heroes of this Earth band together to fight this invading force. These seven are Batman, Superman, Wonder Woman (The first hero to appear in this world), Mr. 8 (Terry Sloan), Catwoman, Robin (Batman and Catwoman's child Helena Wayne), Supergirl and one unnamed hero or 'Wonder' as the denizens of Earth-2 call them.
The ending effect of this Apokolips War ends with Batman, Superman and Wonder Woman dying, all for the purpose of saving the world. With Batman's master plan to shut down the Apokolips towers that control the Parademons accomplished, Earth is able to beat Apokolips back to its own dimension and finally leaving them alone. After this the world rebuilds, idolizing their fallen 'Wonders' with holidays and statues. Five years after the end of the War, Wonders begin to reappear.
Major Story Arcs
The New 52 / Earth-2:
Five Years Later
Wonders such as The Flash (Jay Garrick), The Green Lantern (Alan Scott), Hawkgirl (Kendra Munoz-Saunders) and The Atom (Al Pratt) band together to battle an undead force known as The Grey, the opposite force to The Green, the force that empowers The Green Lantern. Grundy, the avatar for The Grey, begins to reek havoc on Earth after The Green chose it's new avatar (Alan). The heroes band together, even if some are at each others throats- Hawkgirl and Atom, and battle Grundy until Green Lantern places Grundy on the Moon, away from Earth and The Grey. Earth, finally seeing it's Wonders return, is overjoyed. The return continues as Khalid dons the helmet of fate to fight the sorcerer Wotan.
Apokolips forces would launch a second more destructive attack on the universe of earth 2, started by a bizarro version of Superman called Brutaal and the discovering of another kryptonian called Val Zod. With the help of a resurrected Lois Lane as Red Tornado, they discovered the true nature of Brutaal but by then, Apokolips had started a massive attack on the planet than the forces of earth can't not endure. The only option was a massive escape in prepared space ships leaving behind the original planet, now transformed in a host for Apokolips.
The New Earth 2
A group of wonders ended in the extra dimensional world of Telos, during the events of Convergence. As consequence of their actions, Telos became separated from the planet form which was terra-formed into a visually copy of earth and put it in the vibration frequency of the earth 2 universe, in a new solar system of two stars (red an yellow). There the wonders are helping the survivors of planet earth to built a new home and fighting new danger in this new brave world.
Earth-Two of the Smallville show universe .
Clark was sent to the world of Earth-Two, which is the home of Ultraman.
Barry travels to the world of Earth-Two and meet that world's Flash.