Winning

To win the game, you must eliminate all of the enemy armies. There are two main ways to do this: Once an army has no more active members (not including soldiers in recovery or banished) that faction is eliminated. So even if you drive an army from all it's territory, if there are still active soldiers, it may still manage a counter-attack before it finally collapses.
 * Kill and injure them
 * Reduce their respect until they abandon their leaders

Final Score
Your final score is primarily based on how quickly you were able to eliminate all of the other armies. There is also a significant bonus for the difficulty setting you played on. Smaller bonuses are scored for the cash in your bank and if you beat the game with your original duke.