The Injustice League is the name of two fictional teams of supervillains in the DC Comics Universe.
The original (retcon) Injustice League was the brainchild of the interplanetary conqueror, Agamemno. Bored of his dominion, he set out to conquer Earth and their champions, the Justice League. Aided by Kanjar Ro, Agamemno contacted Lex Luthor and they recruited other villain to their cause.
Agamemno then engineered a switch wherein the villains' minds switched with those of the JLA. In the true JLA's absence, other Silver Age heroes came to clash with the now seemingly evil heroes. Eventually, Green Lantern used the power of the Oa's Central Power Battery and a Thanagarian weapon called Absorbascon to reverse the mind-swap.
Having spent time in their enemies' bodies, the villains knew their heroic counterparts inside-out. To regain the edge, the JLA used the power of Robby Reed's alien H-Dial to transform themselves into totally different heroes. Then using his power ring through the Absorbascon, Green Lantern removed all knowledge of the heroes' secret identities from the villains' minds.
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Official Site: DC Comics
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