Suggestions

[Whatever]

Before you declare war you should set some 'war goals' that your faction uses as a casus belli. If you succeed in reaching them, you gain a stability heart. If you fail to achieve them (whether through defeat or a ceasefire), you lose half a heart to a full heart depending on the context. The exception to the latter should be if a war has been officially going on for X amount of years. Once a timer has been run down, a white peace without penalties is allowed.

This would encourage nations to follow through on campaign promises or risk expected penalties, with concessions made for war exhaustion allowing the population to desire a white peace over victory.