The Battle of Arnold was a battle that took place in the city of Arnold (located near the boarder of Shin Makoku) between the Luttenburg division and the Army of Shimaron in the war 20 years ago.
The Shimaron army landed in the south and smashed their way through 2 small countries on the way to Shin Makoku. There was just one city between them and the border, Arnold. If they made their way past Arnold they would easily make their way past the border and it would force them to fight a land battle. And yet, the Shin Makoku army was spread in Grantz and Karbelnikoff territories. They had decided to fight in those two territories and forfeit Arnold.
But when a call for reinforcements came from Arnold, Gegenhuber Grisela advised Stuffel von Spitzweg to send the mixed blood troops there to test their loyalty to country, Shinou, and the current Maou. Stuffel listened and sent the troops to their death.
And so when the Luttenburg division arrived, even with them as reinforcements there was only a total of 4000 troops. The enemy had over 30,000 troops so the winner of the battle was obvious. Even so the Luttenburg division fought hard and lost many men but defended Arnold to the last and so the enemy army was unable to pass. The Shin Makoku army used this to their advantage and moved the troops from Grantz and Karbelnikoff to counterattack and drove out the Shimaron army. It is all because of their victory at Arnold that they were able to reach a ceasefire.