While Bronze Age comics did retain many similarities to their Silver Age counterparts (Superheroes/Fantasy), plot lines became decidedly darker and more adult.
Two books published more or less at the same moment in time serve as the demarcation point from Silver to bronze Age. These books were The Amazing Spider-Man and Green Lantern/Green Arrow.
The seeds of change began with The Amazing Spiderman #96-98, which led to the revision of the code that would ultimately lead to it’s demise as a censorship body. Previously, the Code forbade the depiction of the use of illegal drugs altogether. However, in 1970, the Nixon administration asked Stan Lee to publish an anti-drug message in one of Marvel's top-selling titles. Lee chose to feature a story depicting the negative effects of drug use. In the story, Peter Parker's friend Harry Osborn becomes addicted to pills.
While the story had a clear anti-drug message, the Comics Code Authority refused to issue its seal of approval. Marvel nevertheless published the three issues without the Comics Code Authority's approval or seal. The issues sold so well that the industry's self-censorship was undercut and the Code was subsequently revised.
Not long afterward The Green Lantern/ Green Arrow “Snowbirds Don’t Fly” arc in DC, in which Oliver Queen’s ward Speedy becomes a heroin addict received a letter of commendation from then Mayor Lindsay of NY, and the Code was effectively dead. These stories opened the door to the story that would effectively end the Silver Age of Comics in Spiderman #121 and 122, The Death Of Gwen Stacy.
These industry shaking events occurred during the early 1970’s but the Comics Code Seal stayed around for many years after that and for the most part comics would go along pretty much as they had in the 60’s and 70’s. Marvel gave us characters with dimension and DC’s Batman began to grow up but for the most part, the good guys were good and the bad guys were bad.
The seismic change that we are still feeling today actually came in1986 from the less likely to rock the boat DC comics. It was in ’86 that DC published both Watchmen and The Dark Knight Returns. In one fell swoop, comic readers were confronted by “heroes” who were homicidal, suicidal, sociopathic and borderline psychotic. In short, they were real people. There would be no going back from the changes these books wrought on comic books. We would never look upon our “heroes” in quite the same way.
The “demise” of the Comics Code Authority opened the door to another genre of comics that would help stamp the Bronze Age as a separate and distinct period in the hobby.
In the heyday of the CCA Horror comics simply did not exist! Here is an excerpt from the 1954 Comics Code regarding Horror:
General Standards Part B:
1. No comic magazine shall use the word "horror" or "terror" in its title.
2. All scenes of horror, excessive bloodshed, gory or gruesome crimes, depravity, lust, sadism, masochism shall not be permitted.
3. All lurid, unsavory, gruesome illustrations shall be eliminated.
4. Inclusion of stories dealing with evil shall be used or shall be published only where the intent is to illustrate a moral issue and in no case shall evil be presented alluringly nor so as to injure the sensibilities of the reader.
5. Scenes dealing with, or instruments associated with walking dead, torture vampires and vampirism, ghouls, cannibalism, and werewolfism are prohibited.
You could not even use the WORD “horror”. Vampires, Werewolves, Zombies etc. all simply vanished from the comic book page. About the closest thing to a “Monster” you would find in a Silver Age comic was “Titano The Super Ape” and he was really just a big puppy dog who happened to have Kryptonite vision!
With the dawning of the Bronze Age comic racks were suddenly populated with titles like Tomb Of Dracula, Werewolf By Night, Ghost Rider, and Swamp Thing. Horror was back in a big way. These books (Tomb Of Dracula in particular) were decidedly aimed at a more adult audience. They were heavy on plot and subtle of art with the likes of Gene Colan and Bernie Wrightson .
The Bronze Age would see the revival of the X-Men ( most notably under the pencils of John Byrne). This was a fringe book, on the verge of cancellation when Chris Claremont and Dave Cockrum gave the title the sort of “re-boot” that Neil Adams and Denny O’Neil gave to Green Lantern. Through the Bronze Age the titular team of Mutant Superheroes would provide the blueprint for melodrama and “relationship” based stories. CHARACTERS became more important than plot.
And the single character who dominated the era was Wolverine.
Another fringe title at Marvel would also go through a revival during the Bronze Age. Daredevil. Under the custodianship of Frank Miller, Daredevil would become Film Noir in comics. It was gritty, it was rough and it had a look that harkened to films like the Maltese Falcon and Sunset Boulevard. People died in Daredevil and sometimes the bad guys won.
One commonly used ending point for the Bronze Age is the 1985-1986 time frame. As with the Silver Age, the end of the Bronze Age relates to a number of trends and events that happened at around the same time. At this point, DC Comics completed its special event, Crisis on Infinite Earths which marked the revitalization of the company's product line to become a serious market challenger to Marvel again. This time frame also includes the company's release of the highly acclaimed Watchmen by Alan Moore and Dave Gibbons. However the Bronze Age would reach it’s ultimate height and it’s ultimate end with Batman: The Dark Knight Returns by Frank Miller which redefined the superhero genre and inspired years of "grim and gritty" comic books. While Watchmen is somewhat dated by today’s standards, The Dark knight Returns is so fresh it could have been written yesterday. It was the first true Modern Era book.
Bronze Age comics also offer the collector/investor fertile ground for their particular interest in the hobby. While Golden Age and Silver Age comics are pricing themselves out of the range of many collectors (especially in higher grades), bronze Age books (for the most part) are still very reasonably priced. A collector can still get a high grade run of The Dark Knight Returns for about $100. Many Byrne X-Men and Miller Daredevils come in below $50. Now is the time to pick up your Bronze Age back issues. The prices are already starting to rise. While I never promote speculating, I can tell you that, in general, Bronze Age print runs were much lower than in the Gold and Silver Age, so the long term value of Key Bronze Age books looks good.