For myself, I can identify a number of movements within fantasy history. (I can't call them eras because nobody dominated most eras. I call them movements because multiple movements existed in parallel.)
The Tolkienesque movement began with Tolkien and continued forward. He espoused a full world with its own history. Yes, this world was supposed to precede ours, but you forgot about that pretty quickly.
Beginning with An Interview with a Vampire, Anne Rice ignited the modern vampire movement. This area got red hot in the 90's, leading to the urban fantasy of today.
The D&D movement began with kids playing D&D, and TSR publishing novels in the D&D milieu. Wizards of the Coast has slowed down in recent years, only issuing 4-6 novels per year, but in their heydey, they were a publishing powerhouse. I suppose that all gaming fantasy follows from this. (In my quick research on this, one of the best resources on WotC/TSR is the research I did back in the mid-200's. Go figure! And my work had been ripped off at least once. Yeah, baby!)
I don't know how to trace back urban fantasy. By the time of Buffy the Vampire Slayer, the movement was fully formed. That movement continues to this day with a fierce following.
Then there's the punk. Cyberpunk held supreme in the late 80's to early 90's. Steampunk traces it roots back to the 70's, but as a movement, didn't really get going until the 2000's. Other punks exist as well.
Female-oriented fantasies have exploded big-time in the indie channels. These combine romance, erotica, and the fantastic. For example, a woman meets a werewolf and joins a werewolf pack, along with all the interpersonal drama that comes with it.
Tie-in fiction got real big in the 80s. For example, we only need to look to the vast number of Star Wars novels out there.
I don't think that horror is fantasy, but some folks do. That means that you can't make a history of fantasy without Steven King. He's too big to skip. Likewise, JK Rowling rocked the fantasy world with Harry Potter. I think that you could write an entire book just on trends in young adult fantasy.
Then there's video and how that drives the genres, and the genre drives video. Most recently, we have the rise of the superhero film. In previous years, we had Conan the Barbarian, Xena: Warrior Princess, Buffy, and the great Lord of the Rings revival.
What was hot in what year, and what wasn't? How long were these movements hot before they faded? I wish that I had sales numbers.
I don't know when the fantasy industry imploded or collapsed, rewriting its rules. When were the major commercial crisis? What big hits shifted strategy? What about the modern indie publishing movements? If you're going to give me some history, then give me some history. The documentation is out there, somebody just has to do the work. I don't feel competent enough to write the article myself, so I won't just yet.