Allied forces responded by tightening the rules of engagement, also making it harder for the one-on-one training necessary between coalition and Afghan forces.
Some experts see a silver lining in this new distance between the forces.
"You're at a point where you want to push these Afghan units into the lead," says Michael O'Hanlon, a senior fellow at the Brookings Institution. "Therefore the timing was not as bad as it could have been."
Green-on-blue attacks accounted for about 15 percent of the total U.S. casualties in 2012. They tapered off, but continued through the year and will likely continue in 2013, says Omar Lamrani, military analyst with Stratfor, a private intelligence organization.
The overall brunt of the casualties falls increasingly on Afghan forces as they begin to take on more responsibility for fighting.
"As [ISAF] gets away from the danger zone, we see [Afghan National Security Forces] stepping up," Lamrani says. "Going in to 2012, the big question is, can the ANSF hold it together?"
THE FUTURE OF ANSF
Some government watchdogs don't think so, and repeatedly doubt the Afghan's ability to provide for themselves without allied support. An October report from U.S. Special Inspector General for Afghanistan Reconstruction stated security facilities in Afghanistan will likely not last after the allied planned drawdown in 2014.
Other reports point to waste among U.S. contractors and rampant corruption in the local government.
Of the roughly 180 Afghan Army Battalions, only a handful has ever been capable of operating independently. Some reports number those battalions as few as one. "It's almost inevitable that no Afghan unit could be in that top tier," says O'Hanlon. "ISAF does itself a big disservice by making this metric the most prominent one. It's actually not indicative of anything."
There is no Afghan air force to speak of, and coalition troops are still bolstering the Afghan military's ability to clear roads, among other logistics.
"It's much more informative in Iraq and Afghanistan to look at that second tier," he says. "If these units are doing most of what we're hoping they can do on their own, and doing it effectively and courageously and consistently, we'd be 90 percent of the way towards where we need to be in this business."
ISAF is on schedule to accomplish the remainder of its training efforts by 2014, O'Hanlon says. Training will continue through the roughly 10,000 troops the U.S. will likely leave in Afghanistan after the planned draw-down.
WHO WILL STAY?
The bulk of American troops remain in Regional Command East, or RC-E, in the eastern portion of the country surrounding Kabul. It witnessed 38 percent of the enemy-initiated attacks in 2012, according to ISAF. U.S. Troops are also predominantly in the Southern, Southwestern and Western commands. Roughly a third of the enemy attacks took place in RC-SW, ahead of the 21 percent in RC-S.
"RC-South and RC-Southwest have improved considerably," says Jeff Dressler, senior research analyst with the Institute for the Study of War. "RC-East is still a challenge."
"The key challenge for this year is how well Afghan forces will be able to carry the fight forward in the South and Southwest," he adds.