13 Day War (Demonstone Chronicles #6‪)‬

Massive Federation armies invade Alcea through magical portals. Outnumbered, the Alceans grimly prepare for the bloody conflict, but victory on the battlefield is not good enough for young King Arik. Knowing that Alutar has initiated the war solely to provide a million tears to fulfill an ancient prophecy, King Arik demands that the Knights of Alcea spare as many of the enemy soldiers as they can.