well, nonnel has to finish the hundred years war first, and then there's burgundy, so he has a small, small chance
I suppose if england guarantees the independence of brittany, they might be able to help
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btw, I'm adding the ability to guarantee independence
guaranteeing the independence of a nation means whenever war is declared upon it, you are automatically called to war
it's usually used to deter aggressors while boosting relations, such as the french guarantee of scottish independence