If you were to Wiki the term "Anime Convention", you'll find a fairly accurate description of this strange beast. Originating around 1980 or so, anime conventions spawned off the more popular comic book conventions of the age, and those spawned from even earlier science fiction conventions that started around the 1930s. In that day and age, conventions were a way of drawing authors and fans of the genre together for a day or weekend in order to share their common fascination with science fiction. At the time, science fiction was mainly found in the format of dime novels and compilation magazines, the occasional radio show or movie, and later in comic books. Obviously, drawn comics spawned animated comics, called cartoons, which were for a typically younger audience. As those youngsters grew up, however, they found a need to gather at conventions of their own where they could celebrate all things comic-book related away from the older science fiction group. Comic conventions were created, which eventually drew in the likes of Japanese comics, called "manga" (mahn-ga, not MAN-ga) and the animated equivalent of "anime" (short for animation).
Right around the early 1980s, anime was starting to creep over to the United States in the form of recorded Beta/VHS tapes, many of which were sent over from people who were stationed in Japan as part of the US Military. At that time, things of Japan were starting to take on a new level of fascination since WWII was starting to fade from the minds of many Americans and there were these strange cartoons, books, and foodstuffs starting to pop up around Japanese immigrant areas (Little Japan). People could find sushi and Pocky and these strange adult cartoons that were often of a pornographic nature, but not always of course. ( I'm sure the guys who brought back some of these tapes in the day probably got a real kick out of it while they were stationed in Japan!)
With very few copyright laws surrounding these VHS tapes, the bootleg industry boomed. Comic book conventions were an excellent way to pick up VHS tapes of these strange Japanese anime shows, and slowly the artwork of manga started to trickle over to be translated by comic book companies in the USA. By the 1990s, quite a few of the fans of Japanese comics started spawning their own conventions. These conventions were typically run for an entire weekend, rather than one or two days of the weekend. Often held in a hotel which could be open 24 hours, they would show anime translated by fans (fansubs) and sell bootleg merchandise that could be anything from figures, posters, wallscrolls, whatever could be imported or bought from shops that imported from Japan or China. At the time, it didn't really matter where the fans were getting this stuff, so long as they could get their hands on it!
I came into the anime convention circuit rather late in the game. American comic companies were starting to get copyrights from Japan in order to translate and distribute anime and manga. Funimation was born after the success of Pioneer (which was a Japanese company with US distribution) and MediaBlasters had the corner on hentai (pornographic anime). Many of these companies were reacting to the demand and picking up titles that had not yet been copyrighted. Japan, excited to get their product sold in the USA, started licensing titles to all sorts of up-and-coming companies. Many of these companies would rise and fall, leaving only a few survivors today, but I'll speak on that later.
About the time I was getting into anime, Cartoon network had followed in the footsteps of SciFi (SyFy now) to play the now English dubbed anime. Children's programming such as Pokemon, Sailor Moon and Cardcaptor Sakura were being chopping and recombined into new shows for American audiences at an alarming rate (note, this was done 10-20 years earlier but it started to gain more popularity since merchandising around these shows were so much more profitable to the 80/90's era children). Tokyopop had started printing manga in it's original, although translated, form, rather than the left-to-right format most people read.
This whole huge boom of anime, manga, and conventions reached a head right around the year 2000. A handful of companies were bringing over anime titles to the point there was a new DVD each week, if not more than one title a week. The anime section at Best Buy in my town grew to encompass 16 feet (maybe even more) of 5 foot tall racks: hundreds of titles, with more coming each week. Bookstores went from one 4 foot shelf of graphic novels to entire walls of manga, and at one point Borders even started to buy up manga straight from Japan to sell in some of their locations. Before long there were figures, wallscrolls, T-shirts, posters, bags, stuffed animals and food stuffs and just about every store you walked into. Something Japanese could be found anywhere from the local grocery store to the shelves of Walmart.
The true saturation limit of all of this anime and manga hit right between 2002-2006. For a time there were actual anime/manga stores cropping up in college towns where only normal comic book stores once controlled the territory. Anime conventions could bring in 2,000 people on their very first weekends, and some of the larger conventions were starting to break out in LosAngeles, Chicago, Baltimore, New York, and quite a few other places as well.
But for every good growth period, there comes a downfall. 2008, or the beginning of the "Great Recession" in the USA, suddenly things started to take a downturn. The Blu-Ray/HD Disc war started, and VHS tapes were no longer being produced. DVDs were on the decline. The internet was starting to take over the distribution for anime and manga. During the height of demand, quite a few fans moved to Japan, learned Japanese, or perhaps made contacts overseas. Suddenly there were hundreds of fan subtitled anime, hundreds of scanned/translated manga, and conventions were no longer a place to meet friends, because the internet could instantly connect someone with dozens of others who liked the same things as they did. Japan started realizing that they could make a whole bunch more money if they brought over anime and manga themselves rather than selling the rights off. And especially after the scandals over the many anime/manga sites that were just distributing fan copies all over the internet reached an all-time high. Eventually many of them started to bring lawsuits against this illegal distribution and many companies couldn't compete against the rising prices of licensing Japanese titles.
I always kind of mark the downfall of anime conventions with the death of Big Apple con. I'm not sure what happened there in New York, but for some reason this very large convention died a pretty big death and other smaller conventions started dying off afterward. Maybe it was because every other anime fan thought that he could 'start a convention of his own' and with very little start up money and no financial backing, went overboard and brought themselves into financial collapse. It takes a lot of money and time to start up a convention, and even more to keep it running. I've personally seen two or three 'almost cons' start up and fail either before they even had a single weekend or after that one weekend. The most successful conventions of course were run by business people who perhaps run two or more conventions around the country. With proper financial prowess and dozens of contacts in the industry, these conventions will most likely be the last ones standing when all the other conventions fail.
The true demise of anime conventions today is the stigma of being an anime convention. It might sound strange, but the same thing that used to drive people to an anime convention now drives them away. "ANIME." You wouldn't think the title would mean a lot, but anime conventions are starting to slowly be driven back to their original roots. These conventions must now drop their subtitle. They must reach into the American comic book interests, the pop culture and the cartoons that drive the geek interest in today's world. The younger fans drive the money, and if they think they don't like 'anime', then they'll say so. They won't come to an anime convention unless they think they'll get something from their Marvel universe.
Anime conventions are now being forced to either allow the cosplayers of American comics to compete, or they find themselves shunned by the fan community. There has to be Steampunk and Cartoon Network related things, there have to be memes and trading games. They have to encompass all things "Geek" now just to keep bringing in the attendees. In essence, these Anime Conventions are becoming Pop Culture Conventions.
Will some of these conventions die if they continue on with their chosen category of fandom? Yes. Why? Because the fans are no longer fans of just one thing anymore. That guy over there who likes watching anime also likes Game of Thrones. That girl who reads manga also likes to watch Dr. Who. No one likes just one thing when there are so many things to choose from. Social Media has made staying in touch with others who like our fandom easy. Conventions merely provide a place to socialize in person. Many of these also provide a change of pace and scenery. Conventions are starting to become places to go on a vacation. They have to have a unique venue, unique guests, and interesting vendors to shop from. They have to cater to a wide variety of fans, must have a wide variety of programming, and must continuously find new ways to hit these marks each time.
This, of course, is not to say that new fandoms won't spawn from these conventions. I'm merely stating that anime conventions are no longer the social meeting places they once were. Anime conventions now spawn off other conventions such as My Little Pony conventions. Will these last longer than the series? A few perhaps, but more for collectors rather than fans of the series. Comic book conventions have survived the growth of anime conventions, and they will most likely out-live them as well. Many anime conventions will most likely return to their roots or join back with the comic book conventions of the 70's/80's. Many of them will end when those who run them grow older and wish to deal with families and their futures.
We will probably never see a time again where anime conventions were once the sprawling places where someone could dress up in their favorite outfit and get surrounded by other fans of the series. We won't see 'glomping' or dozens of fans sitting around a room watching a 'new' anime because almost everyone has seen it within the week it was released in Japan. Cosplay won't be limited to just characters coming out of Japan. Video game rooms won't be limited to titles released in Japan. We won't be able to find the vast numbers of bootleg toys and items (which, is actually a good thing) but we won't find the vast numbers of manga and DVD/BDs that we once could in dealer rooms. We won't see artist alleys filled with fan art of our favorite series as now they're limited to mostly original artwork and comics that are more American.
All of these things are in the past. I hope, if you are reading this, you were able to enjoy some of the rise of Anime Conventions, and if you are still attending them now, I have a feeling many of them will never been the same as they once were. My guess is many of them will have fallen to the Pop Culture influences (if they haven't already) within the next few years. Enjoy them while they last, as they are a dying breed.