Marine forces formally took over Sangin yesterday, assuming control of the former Taliban stronghold in southern Afghanistan from Great Britain’s 40 Commando, a Royal Marine unit that has been patrolling the area for months. The change is significant, even if it has received only limited attention in the U.S. mainstream media. The Brits are leaving Sangin, in northern Helmand province, after four years and 106 deaths — 36 of which occurred this year, according to a Daily Mail report out today. Their struggles to establish and maintain security in the district of about 50,000 people has contributed to growing discontent…