I was playing an ironman Japan game in which I vassalized Aztec and Spain declared war on Aztec with the casus belli granted by finishing exploration. I then became warleader and Spain occupied all the Aztec land and my land in the Americas. However, Spain will not agree to any kind of a peace and seem unwilling to try and get 100% warscore. Spain's war exhaustion remains near zero because of lucky nations godly rulers and the length of war modifier seems to have stopped ticking up so it is impossible to make peace.