Weird problem
After loading a game in progress I discovered that my hero army couldn't attack any more. Right click on an enemy & nothing happened. Reloading the game didn't help either. Anyway I had some pioneers nearby so made a city & moved my hero's in thinking maybe when I took them out again all would be well but The new city gobbled them up never to be seen again. That's when I relised my new town was actually the capitol of a new faction & I couldn't build anything in it.