Useful links (where to buy, manuals and such)

[Pocus]

I would advise buying the game at Slitherine, as it will also give you a Steam key, while the reverse is not true:
https://www.slitherine.com/store

There are two manuals, one done by Loki100 (a long time AGEOD veteran) and one by Greu (also an AGEOD player):

English
https://cdn.akamai.steamstatic.com/stea ... 1717061959

French
https://steamcommunity.com/sharedfiles/ ... 3258409021

[ERISS]

On GOG there is FoG:Kingdoms (alone),
and also in a pack FoG2MastersEdition including FoG2:Medieval, usefull if you want to lead the battles on fields (wargame maps): beware it does not include the 8 DLCs maybe needed if you want to use the truest units in those field battles.

[Pocus]

No DLC are necessary to play with all possible units in Kingdoms!