Victory is gained by using the perfect strategy to defeat the enemy. If you incurred heavy losses on the enemy and also gain a strategic victory, you gain a victory. If you lose a huge chunk of your force but rout the enemy, it is a close victory. An example of the "perfect" victory is the Battle of Sekigahara, where Tokugawa Ieyasu destroyed the army of his opponent Ishida Mitsunari with ease because of Kobayakawa Hideaki's changing of sides. His forces were barely hurt while he mauled the enemy and ended the war right on that field. Thus, he gained a victory without heavy losses and not a close victory.