Sieging and demanding tribute ??? help

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I have a few questions for the gameplay of EU:

1.When sieging, how does the 'cover' command work?

2.I can't figure out how it works with demanding a province i tribute. I had a total victory over the Turks and I was sieging Albania, but in the 'offer peace' dialog I wasn't able to choose 'Albania to Spain' (I'm Spain) as a tribute. How come? What does it take to be able to demand a certain province? Anyone knows?

3.One last thing. After my troops had sieged Holstein for a while they stopped sieging and just stood there. Why? Why didn't I take the province? I don't get it. I tried to put more troops in there, but it didn't help a thing...

Hope you guys'll help me out!

 

[unmerged(548)]

1.When sieging, how does the 'cover' command work?

Splits of a large enough (+20%) force to 'cover' the fortress. Lets you draw supply to troops beyond that province in enemy territory.

I was sieging Albania

Sieaging isn't enough, you have to actually conqoure the fortress before it's available.

After my troops had sieged Holstein for a while they stopped sieging and just stood there. Why?

a) Attrition probably reduced the force to lower then the minimum required to siege. Send in more troops.
OR
b) You actually have managed to successfully siege the city and conquerd it. Your now in controll of the fortress and can move away your troops.