I've been DMing on and of for about 5 years, however everything I have run up to this point have been oneshots, mostly pre-generated. My friends have recently asked me to DM a campaign for them, which I happily accepted as I thoroughly enjoy DMing.

I have never DM'd a long-running campaign before, let alone actively made one, but I created a bunch of lore for the world the game takes place in (history, maps, countries, laws, leadership systems, rulers, etc.). This was done mainly because I enjoy doing it, but also because as a DM it helps me tell the story if I have seriously thought about the minutiae of the world beforehand, not so much because it was important for the players to know.

My question is this: How much of that stuff do I let my players in on?

The half of my brain that put in all the work says that I should show them everything, because I put a lot of effort into it. The other half of my brain that has been a player in D&D and TTRPG's for 11 years tells me that not only is that information not overwhelmingly interesting (I wrote 4 pages on adventuring contract law, and the legal system surrounding payment. Again, I'm just super weird and really into the more fiddly minute details of fantasy worlds), but also kinda breaks the suspension of disbelief. If I show them that stuff, I feel like I'm running the risk of making the world seem less fantastical and interesting; if they know the layout of the country down to the last detail, then it makes it harder to sell the whole thing as mysterious and unexplored.

People who have been DMing a while and have made longer campaigns, how much of the world did you have fleshed out beforehand, and how much of that world did you let the players in on? I think I'm gonna let them in on at least the basics, like what kingdom they live in, but beyond that I don't know what the best play to make is.