War index

I'm trying to take control of a country on lu and the war index won't go below 10.00

When you go to the battle screen, on the left you will will see a link that says 'How To Win'. It will tell you how many points you can drop the war index and in what categories (painting, assets, forts, etc.)

You might have to minimize the attack log to see the link.

And on that report you will see the number of index points you can win when invading the country.

This number 10 makes me suspicious.
This is in fact as far as you can get without an invasion.