Answer by Robert Frost, engineer and instructor at NASA, more than 15,000 comics in my collection:
The resurgence was a two-step process.
First, comics producers decided to ride the coattails of the surge in popularity of science fiction. DC Comics went first. They rebooted characters like the Flash and Green Lantern to give them science-based origins. The Flash got his powers in a laboratory accident. Green Lantern got his powers from alien technology. Although Superman came from an alien world and Batman used tech gadgets to perform his acts of derring do, it was more common for superpowered heroes to obtain their abilities through magic and mysticism—like Captain Marvel (Shazam!) and Wonder Woman.
So, science fiction did create a resurgence in superhero comics, but that resurgence, although essential, was small compared to what happened next. The legend goes that Martin Goodman, Marvel's publisher, went to Stan Lee one day and said, "Stan, DC has a superhero team book. It's selling like gangbusters! Make us a team book!"
At that point, Stan was bored and tired. He had always wanted to be a novelist and wasn't being challenged by the pulp stories he was scripting every month in the comics. His wife persuaded him to, just this one time, write exactly what he wanted to write, not what he thought they wanted him to write. And Stan did that. Instead of writing a team book for the 6- to 10-year-olds, he wrote a book for teenagers and college kids. That book was called the Fantastic Four. That kicked off the Marvel resurgence. Soon, Lee, Jack Kirby, Steve Ditko, John Romita, Roy Thomas and others at Marvel were in a creative frenzy, creating books like the Avengers, Iron Man, Daredevil, the Incredible Hulk, and the X-Men.
All of those titles rode that science fiction coattail. How did the Hulk get his powers? Radiation from a science experiment! How did Daredevil get his powers? Radiation! How did Spider-Man get his powers? Radioactive spider! How did the X-Men get their powers? Genetic mutations! And all of these new characters were flawed people, making them more interesting.
But it was the Marvel style of intentionally writing for an older audience that caused sales to increase. Soon, Lee was being asked to visit college campuses all over the country. Kids were reading comics from ages 6-12 and then putting them away and then picking them back up when they went to college. As in World War II, when comics were popular entertainment for soldiers overseas, in the late '60s and early '70s comics were popular entertainment for soldiers overseas. Marvel was working hard to be hip by introducing socially progressive characters to increase diversity. Stories about social issues became more common. DC, always a step behind, but followed that path, too, including a groundbreaking story in which Green Arrow's sidekick became a heroin addict. Soon even the conservative DC had books like Green Lantern/Green Arrow, where writers could tell social message stories that appealed to college kids.
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