Now, my world is old. Very old. And, unfortunately, the story locked me in a paradox. Namely, the colonization of the lush caves featured in another of my questions, which also have a name now (Harat Caverns). You see, a small group of intelligent dragons colonized this place 3.5 million years ago. They were in the renaissance age. How can I prevent them from progressing beyond the early industrial point? And, as a side note, why would they prefer medieval weaponry and customs? Do note that magic does exist.
Edit: Welp, apparently due to bad writing on my part, everyone thinks I'm just talking about the dragon civilization. I'm talking about the entire world. Also, if it helps, the setting is a large archipelago in a mostly temperate zone. I also still want the use of fossil fuels. And there are humans, as well as 8 other races. And the dragons. Sorry about the misunderstanding. Have upvotes as a compensation.
Edit 2: I had an idea. I decided to come up with a special deific monster called a Watcher, or numina. While they've been around for a while, I only just realized how I can apply them to this. You see, numina used to only stalk roads at night, killing travelers, but I realized that perhaps they can prohibit other things as well. Do with this as you will.
Edit 3: New developments! Now, iron is extremely rare, only found in trace amounts in copper ore, and tin is almost nonexistent. Meanwhile, zinc is a bit more common. As a result, brass is used for almost all the things bronze, iron, and steel would be used for. While this may have unforeseen consequences, I do wonder if it would help. Also, I have accepted numina warping, and have decided platinum is immune to it. Also, in response to RobbieGoodwin, who had asked several good questions, what I mean by Numina being "deific" is that they are godlike, but not exactly gods. They are unkillable, but their powers are quite limited, only allowing for a limited, chaotic control over their environment. The temperate archipelago thing was included because I felt that while I may not see any connections, someone else will. Same with other races. And finally for fossil fuels, coal and oil exist, but natural gas does not. And, another thing: this world is completely unaware of air pollution, so that would not be a viable answer.
BTW, here's a link to my chatroom if you're interested in the world.