Not exactly sure what you mean by “non-trash periodic issues,” but I’ll answer the first one.
As with any culture industry, fashions come and go in comics. Prior to 1938, you didn’t really have “superhero” comics per se. Then Superman was introduced in Action Comics #1, sold out a print run of 200,000 copies and in a matter of months was selling almost a million copies a month. Everyone else in the industry scrambled to produce their own superheroes to compete, and you get the Golden Age of superhero comics.

This lasted from 1938 through to the late 40s, especially during WWII when patriotic heroes like Captain America and Wonder Woman were punching Nazis. After the war, however, fashions changed. Superheroes became less popular, and instead romance comics, horror comics, crime comics, westerns, and sci-fi became the dominant trend in the medium.

This gave rise to a moral panic in the 1950s, although more accurately it was part of the larger moral panic over juvenile delinquency. The U.S Senate established a Juvenile Delinquency Subcommittee of the Judiciary Comittee in 1953 to investigate the causes of juvenile delinquency and comics became a major target. While Wertham’s book is best known today for its assertions that Batman and Robin were teaching young boys to be gay and Wonder Woman was teaching young girls to be lesbians, the main focus of the Subcommittee was on horror and crime comics for their depiction of sex, violence, and “subversive” attitudes to law and order.
Fearing Federal regulation, the major publishers established the Comics Code Authority, modeled on the Hays Code that Hollywood had adopted following a similar moral panic about the movies in the late 20s. The CCA’s code specifically banned depictions of sex and violence (among other things), and this basically drove horror comics, crime comics, and (to a lesser extent) romance comics out of business…leaving superheroes as the last genre standing.
Thus began the Silver Age of superhero comics, which started with the intrevitalization of D.C through the revamping of the Flash and Green Lantern and the creation of the Justice League, which brought all of D.C’s Big Three on the same book, but really got under way when Marvel introduced the Fantastic Four in 1961, Spiderman, Ant Man, Thor and the Hulk in 1962, the Wasp, Iron Man and the X-Men in 1963, and then brought all of their biggest heroes together in the Avengers in the same year. Just like happened after 1938, this wave of hugely successful superhero comics led other publishers to try to “follow the leader.”
And so it’s gone ever since: there are periods in which superhero comics wane in popularity or other genres become popular – when alternative or underground comics got big in the 60s and 70s, or the runaway success in the 90s of D.C’s Vertigo imprint which heavily featured British creators working in horror, fantasy, and sci-fi – and then periods where superhero comics surge.


