How does this actually work? When I wip a daimyo in the field and he runs back to his castle I thought I just put my army on the castle and then would be able to assault.

Instead I get a message box asking if I want to abandon or continue the seige.

I am on Easy level (hey, it's my first campaign) if that has anything to do with it.

If anyone can offer advice I would appreciate it.

Regards,
Barkhorn.