Very confused by war score

[xmas]

Playing as England and inevitably in early war with France. I had a war score of about +30, then got a message that Scotland had decided to join on their side and, instantaneously, the war score fell to -20. Looking at the explanation didn't help. To be honest, I don't really understand why I had +30 to begin with, though looking at other discussions I'm guessing it's probably microbattles between vassals adding up. All feels a bit arbitrary though... Does anyone have any insight to offer?

[mikemonger]

Something about war enthusiasm probably. That impacts war score and would have risen in France when a new, fairly powerful ally joined.

[xmas]

Ah, ok. Thanks for this. That sort of makes sense. Although I guess my feedback to the developers is then that when I ship all my troops north, make short work of the Scots and knock them out of the war before returning to France, the French war enthusiasm ought to fall again (and my war score return to positive). Which it didn't! :)