Non-player kingdoms are in every respect exactly like player kingdoms, they have characters, they have armies, they may order their characters to do various missions, their armies to raid and invade, etc. It is possible for a player kingdom to begin the game as the formal ally of a non-player kingdom. For the most part non-player kingdoms are weaker than player kingdoms. Certainly they are not as smart as player kingdoms. It is a good idea not to devote too much of your kingdom's energy towards dealing with non-player kingdoms. Worry about player kingdoms first!