 Elements such as Bizarro, Supergirl, the Phantom Zone, the Fortress of Solitude, alternate varieties of kryptonite, robot doppelgangers, and Krypto were introduced during this era.The complicated universe built under Weisinger was beguiling to devoted readers but alienating to casuals.Weisinger favored lighthearted stories over serious drama, and avoided sensitive subjects such as the Vietnam War and the American civil rights movement because he feared his right-wing views would alienate his left-leaning writers and readers.