War score

From EU3 Wiki

Your War score is basically a rating of how well you are doing in a war. War score is measured in percentage, and is determined by the number of enemy provinces occupied,

If you occupy all of a countries provinces and colonies, your war score will be 100%, while if the enemy country occupies all of your provinces and colonies, your war score will be -100%. Some provinces give a higher modifier to the war score, the population, province improvements, cores, religion and culture effect the percentage gain if occupied. Also, national capitals give a big war score modifier. The war score is only used while suing for peace; the higher your war score is, the more you can successfully demand from the enemy country.