I've just started playing STW, and have a problem which I haven't found the answer to in the manual or the forums.
When invading an enemy province containing an army, I opted to control the battle myself, and found my army on a very empty battlefield.

There was a castle there, but there were no enemy troops visible. I tried marching up to the castle, but there was no reaction. I also tried getting my troops to attach the castle, but again no joy.

I suspect that the next step should have been a seige, but I couldn't find a way to initiate it. I felt like I'd been left at the alter. After ages I gave up, and retreated, just to move on with the game.

Can anyone tell me what I should have done ?