From the game
Syntax: SURRENDER <percentage> MP: 3 Surrender is used to change the percentage of troops your nation loses before surrendering to enemy forces. Any value between 10 and 100% is allowed. Don't be fooled into setting your surrender as low as possible. If two equal forces with different surrender levels are at war, the force with the higher surrender level has a better chance of winning (their troops will hold out long enough for the oppossing forces troops to reach surrender level).
Surrender is critical to Doomsday. It is not only the % of military losses your nation can take but it is also how much of your assets can be lost if you are attacked and lose. In theory if you had 100% surrender you could be killed off in a loss. Be careful with this one.