Welcome to the forum, @Rob_A 
That’s a strange issue 
. The other user that described this problem had found that the culprit was Traveller’s store mod (which is an outdated, very old mod): I can only choose the Ascendancy as a kingdom [SOLVED]
To perform clean reinstalls, delete the Stonehearth folder manually (but make a backup of your savegames, building templates etc first). Uninstalling via Steam may leave some files still there so it wouldn’t be a clean reinstall.
The base .smod files that you should see inside the “mods” folder are radiant, stonehearth, rayyas_children, northern_alliance and debugtools. Anything else would be an external mod. Make sure you have unsubscribed from any workshop mods too.
(And yes, there’s an arctic biome you can choose for the Northern Alliance).