The popularity and circulation of comic books about superheroes declined following World War II, and comic books about horror, crime and romance took larger shares of the market. However, controversy arose over alleged links between comic books and juvenile delinquency, focusing in particular on crime and horror titles. In 1954, publishers implemented the Comics Code Authority to regulate comic content. In the wake of these changes, publishers began introducing superhero stories again, a change that began with the introduction of a new version of DC Comics's The Flash in Showcase #4 (Oct. 1956). In response to strong demand, DC began publishing more superhero titles including Justice League of America, which prompted Marvel Comics to follow suit beginning with Fantastic Four #1. Silver Age