Literally yesterday I was claiming that I couldn't get this to work at all on Windows 10, but now I have, and it wasn't from a guide so I decided to write one. You don't need to install any special patches or mods for it.

I'm very impatient when it comes to installing games and I like things to be very simple. Hopefully, this will help you. I'm also writing this for selfish reasons; if in in two years I want to play again on a new computer, I'll be able to just read this guide that I wrote to get it working.

You don't need to install any patches nor any mods for it (but you should install the 1.0.5 patch anyway).

1. Launch the game for the first time if you never have, then quit it.
2. Install the 1.0.5 patch if you choose to do so (you can do it after the other steps or do it now)
3. Go into %appdata%
4. Find Black Sea Studios
5. Find "Knights of Honor" folder
6. Edit KoH.in2 using a text editor (I recommend Notepad++)
7. Change the width and height to whatever you want. In my case, 1920x1080p
8. If you see "Fullscreen = 0" replace 0 by 1

I split this into two parts because most people will get tricked by a confusing thing about this, the second part is important. At this point it will be working, but you'll think that it didn't work.

Please read part 2.

When you open the game, you'll get the menu where you can pick between multiple screen resolutions that are all 1024x768.

This will look like it didn't work at all, but it did.

You'll have to try them all one by one by clicking the "Test" on each option from the drop down menu.
When you get a fullscreen one that corresponds to the resolution you decided on, then that option will be the right one.
In my case, the second last option is the right one.

If this didn't work and you still get weird behavior, screen cut off, unable to click play... then read the second paragraph of this guide again. You need to test all the 1024x768 options one by one, uisng the 'Test' button. One of them will be fullscreen with the resolution you set even though the option says 1024x768.

In my case, it is the second last option that works.

If you've done this and it still doesn't work, try editing the KoH.ini2 file a again, and make sure you actually saved the modification you made to the file.

Hopefully by now you'll have gotten it to work.

I originally found this in a widescreen/fullscreen discussion thread, but it fixed my 1/3 screen being cut off as well so I decided to write a full guide for it.

Here's the source of the easy widescreen steps:
https://gtm.steamproxy.vip/app/25830/discussions/0/666827974698081759/