Twilight rolled her eyes and prepared herself to explain. "After Equestria demilitarized itself centuries ago, laws were written for what situations an army could be raised in. First is if we are attacked. Second is if we are threatened with war, and third is in defence of an allied nation. The third option is off the table, so to legally create an army, we have to be under one of the first two conditions, and it'll be too late to do so once we are actually under attack."