You can very easily miss this ending if you aren't careful towards the beginning of the game. The only guaranteed way of getting this ending requires you to spare Shaheed at the beginning of the game. Continue through the game as you normally would, until you meet with Shaheed again right before the final mission. During this conversation, he will ask if you are willing to betray America. Say yes, and proceed as you normally would. Also, if Lelend offers a position within Hallbech, refuse.
When you finish the game, the achievement should unlock.