Tanya Seghatchian started working at Heyday Films in 1997. Heyday, a new, small studio, had landed a deal with cinematic giants Warner Brothers as their UK eyes and ears. “Listen,” a friend told her. “This deal will only last if you find Warner Bros the equivalent of the Bond franchise.” Seghatchian was disheartened: until she heard of a children’s book about a boy wizard, called Harry Potter and the Philosopher’s Stone: it was the first of a series.

Warner Brothers were less sure that a children’s series could be the basis for the blockbuster franchise they envisioned. “Family entertainment was not at the centre of film culture in the way it is now,” Saghatchian told the Guardian in 2011. “I knew its appeal might reach more than just children.”

Fast forward 20 years, and it’s hard to imagine a blockbuster landscape without the influence of young adult (YA) fiction. (While the Harry Potter books are not strictly young adult fiction, being sold for ages 7-12 or, in the US, as middle grade (MG) fiction, they increasingly resemble YA as the series gets darker). The Harry Potter series broke record after record – seven years after its release, the last film is still the 10th highest-grossing film of all time.

The success of the series sparked a realisation across film and literature that stories written for children and teenagers had a much greater reach than anticipated, causing a boom in “crossover” YA fantasy. Hollywood began adapting fiction aimed at teenagers with abandon: from fully fledged franchises such as The Chronicles of Narnia, to one-offs which failed to fully capture the moment and whose sequels never emerged: The Golden Compass, Eragon, Inkheart, and The Spiderwick Chronicles to name a handful.

The first Twilight film deal was secured before the first book was even published in 2005, such was the industry’s confidence in the genre. The wild success of both Twilight and The Hunger Games ensured even more YA franchises followed.

But three years after the final Hunger Games film was released, it seems the tide is turning: after a number of films failed to catch fire, there are fewer of them on offer, and the ones that do get a mainstream release are struggling. In 2018, A Wrinkle in Time bombed at the box office, the third Maze Runner film made less than both of its predecessors, and this month’s offering, The Darkest Minds, looks set to lose 20th Century Fox tens of millions of dollars.

“The Hunger Games was so hugely and immediately influential that its particular branch of YA – the science-fiction uprising story – has caught on and burnt out very quickly,” says Telegraph film critic Robbie Collin. “With things like The Darkest Minds and the petering out of the Divergent series, both of which were hugely derivative of The Hunger Games, we’re now at the stage of the genre’s life cycle where the whole thing feels completely played out.”

That’s not to say YA in general isn’t still booming – it’s simply navigating the trends and shifts of any established genre. In the last five years, audiences have turned away from blockbuster fantasy franchises to YA films set in our own reality, finding drama in obstacles real teenagers may face. That trend began with the huge success of The Fault in Our Stars, which was soon followed by Paper Towns, Everything, Everything, The Spectacular Now and Me, Earl and the Dying Girl.

Now, the adaptations succeeding in an oversaturated pop culture landscape are of non-fantasy YA, including streaming hits such as 13 Reasons Why, The Kissing Booth, and To All the Boys I’ve Loved Before, which tallies with trends in publishing. Of the Top 10 bestselling YA books of the year so far in the UK, only two are fantasy.

Most of the others see protagonists dealing with real-world issues: Karen McManus’s One of Us Is Lying begins with a boy dying in detention, thanks to a deadly peanut allergy. Becky Albertalli’s Simon vs the Homo Sapiens Agenda is about a teenage boy coming out, and has already been made into a successful film, Love, Simon. And Angie Thomas’s The Hate U Give, which has a highly anticipated film adaptation due in October, and has won several book awards, is the story of Starr, a black American teenager who watches as her friend is murdered by a white police officer.

So have the producers behind the fantasy films of 2018 simply missed the moment? If 2018’s film version of 2014 thriller The Darkest Minds comes too late, then upcoming adaptations of the much-loved Artemis Fowl and Mortal Engines series, which began publishing in 2001 and 2003 respectively, feel aimed at a totally different generation to the readers who first loved the books.

Anna James, a books journalist and author of the upcoming children’s book Pages & Co, says she doesn’t see a clear shift from fantasy to YA dealing with contemporary issues. “Arguably the biggest YA release of this year is Tomi Adeyemi’s The Children of Blood and Bone,” she explains, “which is epic fantasy, and has already sold screen rights.” Instead, she argues that dips in the performance of fantasy novels and adaptations have more to do with the fact fantasy stories are “hard to pull off without being derivative”.

Collin agrees that an original and unpatronising fantasy franchise could still flourish in the current landscape. “The genre boomed in the first place because it treated its target audience with a respect they hadn’t previously been afforded, so as long as the forthcoming franchises do likewise, I’d imagine they have every chance of commercial success. They just have to look for inspiration outside of Twilight and The Hunger Games.”

For YA author Holly Bourne, ultimately, it’s the ability to speak frankly to audiences about complex, real-world issues that makes a YA story a success, across fantasy, sci-fi, thrillers and dramas. “Teenagers are continually undermined and underestimated: every successful YA book and film is so because the creators refuse to patronise them, telling them the truth about what it is to be young.”

But Bourne does see one common thread emerging across YA fiction of all varieties: social justice. “I go into schools a lot to talk about my books, and teenagers today are so politically engaged and brimming with energy and an urgency to fight for a fairer world. The success of The Hate U Give and The Hunger Games reflect this anger and it’s really exciting to watch how art stokes teenagers’ political fire. Stories really can change the world, and it’s a brilliant time to be writing for this age group.”

James agrees. “Teens have always been keen for voices that are inspiring and progressive, people finding out what they believe in and standing up for it, whether it’s allegorical, or explicit.”

Though a lack of diversity in YA is still an issue, particularly in the UK, many of the bestselling YA books of the last two or three years have centred around racism, homophobia, transphobia, and misogyny, from Nicola Yoon’s The Sun is Also a Star, to Lisa Williamson’s The Art of Being Normal, to Asking for It by Louise O’Neill.

If any unifying thread can be found in the most successful YA films of the last two decades, perhaps it’s a shared narrative of love triumphing over oppression, with Harry Potter analogies refusing to disappear from millennial discussions of politics. But looking at the last 20 years of YA film in this light also shows how far we’ve come: from a feminist perspective, Twilight seems dated at best; while The Hunger Games was praised for its revolutionary politics on release, it would have been hard to imagine a film aimed at teenagers that frankly discusses racist police brutality in the US, like The Hate U Give, making it to screens in 2012.

“Young adults are only getting more politically and socially engaged,” James insists. “The books and films dealing with these issues are only going to become more prominent.”