This is amazing to see! I've wanted a good, digital, historical atlas for more than 10 years. The ones I've seen have all had some kind of limitation that's made them less-than-ideal imo. This one seems to check most of my boxes in terms of features & UX, plus it looks really nice! Big kudos to everyone involved. I will definitely be using this a lot!

That said, seeing it IS a definitely bittersweet since I started my own version of this about a year ago (after giving up on something nice like this ever showing up). Being a hobby project it's far from being able to match the progress that this has made. Now I don't know if it's still worth to pursue, which is both sad but also nice since I can do other things and take pleasure in using this without having to worry about actually making it myself...

Some features that I had (or was planning to have) that I think would be very nice, for inspiration; in case you're interested:

- Allowing anyone to add and edit data. One of mny gripes with many of the existing digital atlases was that they were very bare bones in terms of how much content they had. I hoped for a "Wikipedia for historical maps" kind of place. Maybe not at all what you envision and maybe your setup is too complex to allow for it, but I wanted to mention it at least. But at least your feedback system was very nicely integrated and easy to use, so hopefully that'll be good enough (and spare you the pain of having to care about trolls and layman mistakes).

- Showing hierarchical Regions instead of just 1. For instance, being able to show the Holy Roman Empire above its various duchies/principalities etc, and those above their various counties etc. It feels overly simplistic to ONLY show topmost Region. And quite often there's not even any single Region that's undebatably the "topmost" either.

- Generic "Events" for things that aren't battles.

- Events or something similar to explain what's going on whenever a Region's border changes, a Region appears/disappears, a Region changes name etc. Basically connect the change you see on the map with a link to learn more about what caused that change. I think this is super valuable when it comes to going from "cool, that country grew a lot there" to "so what actually happened?".

- The search field seems to be connected to modern-day places rather than historical Regions. For instance, I expected being able to search for "Kalmar Union" to get to the place and time of the Kalmar Union. Or to search for "Alexander the Great" and go to his time and place. But kudos for supporting native spellings of place names, like "København" for Copenhagen.

- I see that some battles have a corresponding war underneath their names, which is really nice. I would love to be able to filter/find/highlight all battles from a given war. That way it would be a LOT easier to get a better grasp of the extent of a given war. I'd also like to see the war's duration and its belligerents.

Then some UX feedback and bugs I noticed:

- Showing the modern-day names of cities before they exist feels pretty weird. It can help for users to navigate and understand where they are, but I think it would be very nice to at least have an option to turn them off. Ideally also to have them show up only after they've actually been founded. A bonus would be to also show them with their historically accurate name.

- I notice that you see the name of the Region currently in the center of the screen, but I think it'd be more useful to show what's at the cursor's position. Especially when you have a bunch of small Regions. If you tied it to the cursor you could also highlight the currently selected Region.

- The red box for the current year looks reeeeally draggable to me. I would combine it with the slider.

- Having keyboard commands for going forward/backward with the time slider would be really nice, to complement when you're panning around with the mouse.

- I totally understand where you're going with showing BC years as "-X", but it looks pretty weird. Especially when it's outside the time slider, like underneath the names of people.

- Also, there's no "year 0"; it goes directly from 1 BC to AD 1.

- When there are multiple overlapping things (e.g. all the battles in Italy during the 80s BC) it feels a bit random which gets shown. It's also not clear that there are stuff that gets hidden until you zoom close enough.

- If I open a wiki page for a battle and then click a link in the article, I'm then unable to return to the original wiki page. Clicking on the battle again does nothing. I have to either close the wiki sidebar or click on another battle first.

- There's no way to close the Maps sidebar except by opening the wiki sidebar?

- Closing the top panel (the one with Regions, Rulers, People, Battles) causes the Maps sidebar to pop out. Feels weird; I was expecting the top panel to get minimzed similar to how the wiki and Maps sidebars are in their inactive states.

Sorry for the length of this post, but I just had a decade of thoughts to get off my chest; not to mention a year of spare time work on doing almost exactly what you have here. Whether you take any of my feedback or not, thank you so much for making this!