Worldbuilding is one of the most difficult challenges an author can face. It’s a multifaceted problem as it requires a full and clear understanding of the setting being developed for the story to function within. It’s even more difficult when the world the story takes place in is entirely fictional. To consider the complexity a written world can have, The history of the real world can serve as a great example of how anything and everything can be connected in an intricate web of international connections. It’s even more complicated when adding on to an already established world through adding on to the worldbuilding already established via a sequel. Especially in respects to sequels, additive worldbuilding can prove to be a difficult challenge but can create a far richer story.
There are risks that can be found when adding more to the setting already established. The main risk is that any new additions could contradict already established rules of the world in the previous story or potentially feel disingenuous. How does worldbuilding ever feel disingenuous? Often it can be some seemingly random addition to the story to justify a new power, ability, tool or general convenience for either the protagonist or the antagonist to further the story. It can make the story feel contrived as seemingly random things pop up almost in a Deus Ex Machina style that feels like fate is being cheated. This can be avoided with proper set up in earlier chapters or even books to plant those seeds. While I did enjoy the Harley Merlin series by Bella Forrest at first, there was a point where things kept being added on to the magical world in a way that kept feeling a bit too convenient to keep the plot going. This went for both Harley and Katherine as it felt more like extending the already long story rather than building upon the magical urban fantasy world.
But additive worldbuilding serves to strengthen the story by adding elements to the world that strengthen and further the story. What makes it different from feeling contrived or convenient to furthering the plot is that it’s adding on to something that was either hinted at earlier or already present in previous books. The main thing is that it’s not something that feels pulled out of thin air to create tension or additional plot points to arbitrarily lengthen a story. A really good example of this would be Skyward #3 – Cytonic by Brandon Sanderson where the main focus was on a major story element in the first two books and finally explained in the third. It’s something clearly established in the world, adds to the mystery and the intrigue of why it exists, and by the end of Cytonic, it builds upon the world in a way that satisfies the interest and curiosity of the reader.
It’s tricky to determine what is and isn’t appropriate when adding on to existing worldbuilding. It’s a situation that requires very careful consideration of explaining something that shouldn’t be explained. There’s a beauty in things that are unexplained, that add to the mystery and fascination of the world as it creates wonder and curiosity in the reader. It’s very dangerous to add these explanations as it can either make something far less interesting or, in a worse situation, retcon what was already established. A very famous example was the whole medi-chlorian explanation in Star Wars to try and explain how people could use the Force. It just ruined the mystery of what was a mysterious and magical, well force.
But what might be a more nuanced example of adding too much to destroy a world was in Avatar: The Legend of Korra when there was greater emphasis on explaining the spirits. The thing is, in every other iteration of Avatar (at least the ones I’ve experienced), the spirits are independent of morality and often work in tandem with the balance of nature. In Avatar: The Last Airbender, the spirits were often their own things, focusing on their own existence and the environment they inhabit. This is also the case with The Chronicles of the Avatar where the history of the previous avatars, Kyoshi and Yangchen, have spirits included as well, but they’re never the main focus. They exist to supplement and add to the story to create a consistency in the Avatar universe. The Legend of Korra broke this worldbuilding by dedicating a few episodes to try and explain the nuance of the spirits while still maintaining some mystery to what they are. It doesn’t work as it just makes the spirits simply another faction rather than this mysterious aspect of the Avatar world that made the Avatar’s interaction with the spirit world fascinating and open to anything. It tried to apply a hard magic system to an already loved and appreciated soft magic system, damaging the overall world established within the Avatar universe.
To understand what works as additive worldbuilding to strengthen a story, a writer must consider some very valuable questions. “Does this matter?”, “Does the reader need to know this to get the most out of the story?” and probably the most important thing “Does the story suffer if I don’t include this?” Building upon the world through sequels and, in some cases prequels, can help to make the world fascinating and more engaging. But something to also consider is even just hints at more in the world without ever going deep into it not only allows for future story potential but also creates mystery and interest the readers may have with everything surrounding the main story.