UPDATE (2016/08/22): Since this is such a popular post and is still one of the top results for how to install the mod, here are the updated instructions:

If you, like me, bought the game from macgamestore.com way back in the day, they’re no longer updating the game for whatever reason. Thankfully, if you go into your purchase history, they give you a Steam key that you can redeem on Steam for the latest version of Crusader Kings II. Now onto the instructions:

Note: This entry does not relate to art or design, in the traditional sense of my site. I am writing this to help others that have run into similar problems.

Background

If you’re like me, you might have heard about the game Crusader Kings II through Penny Arcade TV’s Extra Credits show in an episode called Games You Might Not Have Tried #4 and you might have thought, “hm, that looks like a really neat Civilization-type strategy game with a pretty rich story…” But then the narrator said, “Game of Thrones mod…” and you were hooked.

Now, as a primarily console-based gamer, I have to take deep breaths when I hear about a cool PC game because odds are that it won’t work on my Mac, but luckily, in this case, Crusader Kings II is available for PC and Mac, so I went ahead and bought my copy from the Mac Game Store. I downloaded my copy of the Game of Thones mod here, but you can do a quick Google search for the latest version if you’re reading this post months after I wrote it.

Because I purchased my copy of Crusader Kings II through the Mac Game Store, it was a direct download and all I had to do to install the game was drag the app from the .dmg file to my Applications folder. This is where the trouble starts, if you bought the game to play the Game of Thrones mod.

The issue

After figuring out where to put the mod, when launching the game and selecting the mod, the game crashes instantly. This is because the path specified in A Game of Thones.mod doesn’t point to the actual folder with all of the mod’s resources like it should.

The 5 minute solution

It turns out, this isn’t an incompatibility between the mod and the Mac version of the game, it’s an issue with a directory in the A Game of Thones.mod file itself, which was developed by a team who had assumed the mod would be used by a PC user and hadn’t been able to test it on a Mac. Here are my step-by-step instructions on how to get the mod working on your Mac in less than 5 minutes:

Steam users: If you bought your copy of Crusader Kings II through Steam, I’ve added steps to the instructions below to get the mod working for you as well. There may be a few extra and unnecessary steps, but I recommend you follow them all because as inelegant as they may seem, they work. Follow the steps as written originally unless you see a Steam heading below the original step.Note: The Steam portion of this guide was made in collaboration with my commenters. As I don’t own the Steam version, I can’t test these steps personally, but they have worked for others. If you find a way to optimize them at all, comment and let me know.– Steven

Step	Action
1	Unzip the A Game of Thrones mod.
2	Go to your applications folder, find Crusader Kings II, right-click it and select Show Package Contents.Steam: Skip this step, go to step 3.
3	Navigate to Contents / game / mod and copy all of the files from the original ZIP here. Screenshot of Crusader Kings II package contents Steam: Navigate to Library / Application Support / Steam / Steamapps / common / crusader kings ii / mod / and copy all the files from the original ZIP there. (The copied files within the mod folder should still look the same as in the screenshot above.) If your Library path is hidden, in the Finder, click on the Go menu and then hold down Option or Alt on your keyboard and the Library will appear in the list. Click on it to navigate to Library.
4	Open the file A Game of Thones.mod with TextEdit.
5	In the Path field, replace the directory “mod/A Game of Thones” with “/Applications/CrusaderKings2.app/Contents/game/mod/A Game of Thones” and replace user_dir with #user_dir. Screenshot of A Game of Thones.mod in TextEdit with changes Save the file and exit TextEdit. It might be locked and ask you if you want to overwrite the original or create a duplicate, make sure you overwrite the original. Steam: In the Path field, replace the directory “mod/A Game of Thones” with “Users/YOUR USERNAME HERE/Library/Application Support/Steam/SteamApps/common/crusader kings ii/mod/A Game of Thrones” and replace user_dir with #user_dir. Save the file and exit TextEdit. It might be locked and ask you if you want to overwrite the original or create a duplicate, make sure you overwrite the original.
6	The next time you run the game, select the A Game of Thrones in the Select mods to play field before you select Start CKII.Note: The game may still crash the first time you do this, but if it does, launch it again and it will work.Steam: Unzip the A Game of Thrones mod again and this time, do not modify the A Game of Thones.mod. Navigate to your Documents folder and open the Paradox Interactive folder. Open the path to Crusader Kinds II and create a new folder inside named mod. Copy the contents of the unzipped A Game of Thrones folder to this new mod folder. Perform the “normal” step 6.
7	Enjoy playing out Robert’s Rebellion, and good luck avoiding marrying one of Walder Frey’s hundred children!