Here's what Firefly says about the expansion pack:

Rise of The Wolf is a special game mode featuring classic Stronghold characters, improved AI and new PvE (player-versus-environment) gameplay. After being assigned a starting location on a medieval map of the British Isles, players are forced to hold back an AI invasion from The Wolf, The Snake, The Pig and The Rat. The Wolf has returned to take vengeance against the people of Britain, forcing players to take back villages by engaging enemy troops and winning votes in the political arena to gain control of vital land. These new AI opponents have similar abilities to regular players, allowing them to raze and capture player villagers, vote for themselves in elections, repair castles, scout resources and more.

Stronghold Kingdoms was released for the Mac in January, over four years after it first appeared on Windows PCs.