How do I know if I should add an idea to a book?
Question: This is kind of an opinion question I guess but I'm just not sure what to do or well if it would work. Ok so my story idea is about different kingdoms and one of them takes over the rest of them or well most of them. I keep thinking of this as fantasy because I'm creating another world but I also don't think it is because there's no magic or monsters so I feel like I need to add those but then they don't seem to work because it wasn't supposed to have monsters. Today I thought of an idea that the bad guy is like a wizard and that's why he's able to take over the kingdoms so easily and why he can control people. I was also going to add this dark forest where no one has ever survived a night in there because there's a darkness that gets them. The people would know about magic but it's frowned upon and they don't like people with magic there's also not a lot of people that do magic. The only real magic would be like the bad guy and his son and the darkness. Does that sound good or to weird? I'm afraid if I add this stuff that people will be like that wasn't need that it was just thrown in there and didn't make sense. Will I have that problem? Do I have enough to make it work in the story so that it doesn't seem like it's just random but actually belongs? Like if the world was totally normal but then there was magic but had nothing to do with the story it would be totally pointless. Is this idea pointless? Should I just keep it as a
normal world as I first had it? I like both ideas but I'm afraid the one might not work. I know in the end it's my decision but I just need an opinion on this I guess.
At the risk of stating the obvious, either version could work, but no version is right if it doesn't feel right to you.
Anytime the story you're writing feels wrong or like it doesn't make sense, treat that as a warning sign that it will probably not make sense to the reader either. Similarly, if some element seems unnecessary, it probably is.
Most fantasy worlds do involve magic or technology that are forbidden by the physics of the real world, or life forms that do not exist--and that's why the author creates a fantasy world. It's as if you say, "I wish unicorns were real. I know, I'll imagine a world in which they are."
However, you may have another reason for creating a fantasy world. Maybe you have an idea for a culture that doesn't/never has existed, or an environment, etc. Magic and monsters are not required.
On the other hand, if you do have a reason for a wizard and a dangerous forest--if they feel right to you--by all means use them. But don't just include them because you think you should. If you're not passionate about them, it's very hard to write in a way that will engage the reader's passion.
Also... you may find in the writing that, when the moment comes, a fantasy element will feel right or wrong. And you may also find that you don't know for certain until the second or third draft. So don't feel you have to have all the answers right away.
Best of luck.