It can seem hard to imagine now, but back in midcentury America, trying to find people who shared your interests was not as easy as opening a laptop and diving into a comments section or a subreddit. Especially if you were an adult and liked superheroes and comic books.

Despite the 1960s’ famous counterculture, most people in that era still followed the rules of conformity. Some of those unspoken rules were that science fiction and comics were okay for children, but after high school those passions should be set aside in favor of grown-up pursuits.

Then came Comic-Con.

The last decade has seen an explosion in the geek and nerd sector, and the convention has turned into a pop culture mecca the size of a small city.

This summer marks 50 years since three comic book enthusiasts created a first-of-its-kind comics convention at San Diego’s U.S. Grant Hotel to bring people who loved comics together. Now the annual gatherings, known as Comic-Cons, are held all over the world, though San Diego hosts the biggest, which starts Thursday.

The cultural landscape has changed dramatically over the last half century, and San Diego Comic-Con, or SDCC, has morphed along with it. The last decade has seen an explosion in the geek and nerd sector, and the convention has turned into a pop culture mecca the size of a small city for an extended weekend.

While that has been a hugely welcome development for science fiction and comic book fans, in some ways Comic-Con might be a victim of its own success. The gathering is once again contending with changes as production companies begin to no-show rather than get lost in the crowds of one giant convention, with companies like Disney even starting to host their own conventions.

But back in 1969, the problem was too few opportunities to congregate with like-minded fans, rather than too many. Those adults who still clung to their comics and sci-fi shows had to turn to long-distance mail to connect across the country. SDCC’s founders, Sheldon Dorf, Richard Alf and Ken Krueger, all started out as comic book dealers who sold their wares by mail order. The only adult among them, Dorf, 36, convinced Alf, Krueger and the teenage comic readers and dealers he was hanging out with that they could put on a convention instead of growing up.

Though the idea from the beginning, according to the conference’s website, was to create an event that took a more expansive view of fandom, the early years were focused on comic books — in particular Marvel Comics and DC Comics — and the population that came was heavily white and male.

The first event featured the late Jack Kirby, famous for creating the characters who eventually became the Avengers, including Iron Man and Captain America, along with Black Panther and the Fantastic Four. The other guest was Ray Bradbury, who was convinced to attend after being told the event was a nonprofit and showing up for fans would be a public service. (San Diego Comic-Con International remains a nonprofit organization to this day because it had to become one after Bradbury said yes.) It was a small affair, with some 300 attendees, but in those days, numbers like that were a wild success.

SDCC has ridden the waves of pop culture ever since. First, it moved from hotel to hotel until winding up at the San Diego Convention and Performing Arts Center as the ’80s arrived and the attendee levels rose to between 5,000-6,000 people on average. Then it underwent an explosive growth surge as comic books began taking to the big screen, beginning in 1989 with the release of “Batman.”

Today, the convention takes over the entirety of the San Diego Convention Center, hosting more than 130,000 attendees over a five-day span. The new century has been especially good to the event: The arrival of Marvel Studios and hit fantasy TV series such as “Game of Thrones” and “The Walking Dead” have driven attendance skyward, while production companies from Disney and Universal and television producers from NBC to HBO have used the convention to promote any TV show or film even remotely “genre-leaning” in a bid for fans’ attention.

But last year saw attendance fall for the first time, as some of the more prominent companies began skipping the event. Though the Marvel Cinematic Universe (henceforth the MCU) has a panel this year, where fans assume producer Kevin Feige will announce the first few films coming in the post-“Avengers: Endgame” landscape, there is a sense it was a last-minute choice by Marvel parent company Disney that came late only after rivals at Warner Brothers and the DC Extended Universe said they would not attend, clearing the way for Disney to dominate.

Warner Brothers’ absence is due to the “DC Comics universal franchise” it envisioned failing to gel, as well as the delay on the next “Fantastic Beasts” movie after the last one failed to get the rave reviews of the original “Harry Potter” series. And after this year, there will be no “Star Wars” films released until 2022. On the TV side, “Game of Thrones” ended with a controversial set of twists, and HBO has not yet announced if a potential spinoff will be picked up. (Moreover, it’s bringing no one to SDCC who would make such an announcement.)

Even if the fantasy era of the 2010s doesn’t make it to the next decade, SDCC will simply continue to morph with the times.

With other potential shows like “The Wheel of Time,” (Amazon), “The Witcher” (Netflix) and “The Broken Earth” (Turner Networks) all getting snatched up in the streaming wars content arms race, the nerd pop culture bubble could be ready to burst.

But will that really be the collapse of SDCC? Anyone who has attended a comic convention in the last few years knows the answer is probably no. Where once these events were filled with white dudes obsessing over comic books, the floors are now far more diverse. Families dress kids up as their favorite superheroes, treating a trip to the convention as a perfectly normal family outing where everyone can let their geek flags fly. Even if the fantasy era of the 2010s doesn’t make it to the next decade, SDCC will simply continue to morph with the times.