why did batman fight superman in dark knight returns
The Dark Knight Returns Superman diverts a Soviet nuclear warhead which detonates in a desert, nearly killing himself in the process. The United States is hit by an electromagnetic pulse as a result and descends into chaos during the resulting blackout. In Gotham, Batman realizes what has happened, and he and Robin turn the remaining Mutants and Sons of the Batman into a non-lethal vigilante gang. He leads them against looters and ensures the flow of essential supplies. In the midst of the blackout, Gotham becomes the safest city in the country. The U.S. government sees this as an embarrassment, and orders Superman to remove Batman. Oliver Queen predicts to Wayne that the government lackey Superman and the maverick Batman will have a final confrontation. Superman demands to meet Batman. Knowing he may die, Wayne chooses Crime Alley, where he first became Batman. He relies on Superman's weakness caused by near-death in the nuclear blast (Superman only just managed to survive by absorbing the energy of the sun, but he is still vulnerable to attack).