If the mod isn't working properly, it is possible that there is an issue with the .mod file the submod came with. The following steps should fix the problem:

1) First find the cultofmarx .zip file in Documents/Paradox Interactive/Crusader Kings 2/mod

2) Using something like winrar (which you can find online for free), extract the files and put them in a regular folder called "cultofmarx" (you should have Documents/Paradox Interactive/Crusader Kings 2/mod/cultofmarx)

3) Using something like Notepad++ (which you can also find online for free), edit the part of the cultofmarx.mod file that reads:

dependencies=
{
After the End Fan Fork
}

to:

dependencies={"After the End Fan Fork"}

4) If the above is still not working or problems persist, it's possible that being subscribed to the mod on Steam is overwriting the .mod file. Try unsubscribing, but only after favoriting and rating the mod five stars.

P.S. This probably doesn't work on a Mac.