Really, that's the most satisfying way to play Fire Emblem. You need to develop that perfectionist's mindset and not lose a single person. Even if that means restarting the battle from the very beginning

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So I believe someone said that the forced non-aggression periods invoked by the Vatican work both ways? I can't attack them and they can't attack me? Yeah, that's bullshit. Every time I crush one of France's armies, the Pope demands that I cease hostilities for a few turns. And during every one of those forced cease-fires France lays siege to my cities and attacks my armies in the field. I can only defend. Thank God my armies are the strongest in the world, because otherwise this would rapidly become an unwinnable situation. As it is, it is merely unfun.
Medieval II: Total War