Imperium

The Imperium are a race of parasitic aliens that explore the galaxy to conquer other planets. Several centuries before the 21st Century, the Imperium invaded the planet Mars and wiped out almost all of the Martian population and copying that races shapeshifting ability. The Imperium would have continued on their path of conquest if not for the intervention of a small band of surviving Martians, who used a rare plant to place The entire Imperium force in stasis. The only survivor of the task force, J'onn J'onzz, remained on Mars to ensure the Imperium would never be released

Several centuries later, two astronauts from the planet Earth travelled to Mars and accidently released the Imperium while J'onzz was hibernating. The race picked Earth as their next target and began infiltrating the planet with shapeshifting duplicates of real people. Some of these duplicates undercover at Wayne Technologies came under suspicion by Batman who attempted to subdue them while they sent a signal into outer space. Batman recieves assistance from Superman, who experiences a strange vision during the fight and collapses. The building is then blown up by the shapeshifters, who walk away unharmed despite serious injuries. Several days later the Imperium army begins their invasion of Earth, covering the sky with dark clouds to allow them to attack. Batman and Superman begin fighting the invaders, when Superman has another vision, and realising its meaning, flys away to rescue J'onn J'ozz, who was held captive by the Imperium. Batman follows Superman and both of them fight an army of Imperium soldiers, with help from fellow heroes Green Lantern, Flash, Hawkgirl and a new hero, Wonder Woman. The heroes discover the origins of the Imperium from J'onzz, and then team up to fight the aliens. All of the heroes are eventually captured except for Batman, who is believed dead, and taken before the Imperium leader. The leader tortures J'onnz and nearly kills him when Batman returns and sabotages the crystals controlling the gas factories, shining the suns rays on the Imperium. The leader attempts to retreat in its spaceship but is attacked by Wonder Woman and Hawkgirl and crashes. The remaining aliens are then defeated and Earth is safe. These heroes then decide to form the Justice League to protect Earth from other threats.