Read the instructions on page one!!!
Advice: If you have crashes with the 3.6 Starting Armies Startpos, try using the 3.6 no starting armies version.
II. BETA TESTING CAMPAIGN SELECTION for experienced users that want to experiment:
Due to bugs with the present campaign files (startpos) we have provided several versions of the campaign files for you to choose from. The latest versions are more immersive and enjoyable, including some starting armies and forts (3.6 Starting Armies), but will have campaign crashes at certain point. The older campaign files are probably more stable but have several inaccuracies and are likely less fun (3.4 and 3.5)
Due to the lack of a new launcher you will have to manually select which version of the campaign you want to play.
Different campaign files are available in Program Files (x86)\Steam\steamapps\common\Empire Total War\ACW\SubMods\ZoR\WPATH\CS or US.
Copy the files from any of the 3.4, 3.5 or 3.6 subfolders that you wish to use into
Program Files (x86)\Steam\steamapps\common\Empire Total War\ACW\SubMods\ZoR\WPATH\CS or US
and into
Program Files (x86)\Steam\steamapps\common\Empire Total War\data\campaigns\ACW_WPATH\CS or US
Don't worry, it only looks scary, but it really isn't.