It's not as easy as it might seem
I also had Spain, however, France declared war against me, so I decided I was fed up with them and sent 4 of my forces up to take Flanders/Alsace Lorraine/Paris etc, to totally wipe them out. This meant I had no forces in Madrid, and of course, in my absence, they rebelled, and took the capital again...so I am currently assembling a new army to go take them again.
Problem is with Empire Total War is that you cannot advance with a 'blitzkrieg' approach - not unless you have the forces in which to do that. Major powers such as France, if you conquer them, will have a high public unrest for about 10-15 turns, so that means unless you have a big wedge of money, you can't steamroller other countries until public unrest is low.
Another problem is that countries such as Prussia or Austria, for example, when they expand, they take lots of different areas here there and everywhere. So, that means you have to conquer each little bit to wipe them out, which makes life very hard, whilst you try and squash rebellions and fight their armies.
Not only that, but sometimes you just can't take countries when you want to...since if everyone dislikes you, you will be getting punched by lots of angry countries from all sides
...so it is a slow process at times
Jack
p.s. I downloaded it last night Lars, but haven't got round to installing it yet. I'll let you know as soon as I install it