Last week's shooting death of a two-star American general by an Afghan soldier is another tragic example of the continuing dangers of Afghan service. It also demonstrates the occasional difficulty in differentiating allies and enemies in that part of the world.

Maj. Gen. Harold J. Greene is the senior American officer to be slain in Afghanistan. Fifteen other NATO troops, eight of them American, were wounded in the attack. That number included a German brigadier general.

The shooter, described as "a terrorist wearing an Afghan army uniform," was also shot and killed.

The attack took place at Camp Qargha, the Afghan Military Academy, 11 miles west of Kabul. The Taliban hailed the general's assassin as a "hero soldier."

There have been more than 85 of these "green on blue" attacks on coalition forces by the Afghan military in this long and inconclusive war. They peaked in 2010.

But it is reasonable to fear a resurgence of attacks on foreign military "advisors" deployed to train the Afghan army and fledgling air force, particularly after the Obama administration announced plans to withdraw all U.S. combat forces by year's end. Pity those non-combat troops slated to remain.

Similar such attacks, though relatively rare, have occurred in other U.S. wars as Americans disengaged. In Vietnam, it was far more common for those we had trained to simply wander off or fail to report for duty when trouble was brewing.

This should not be taken as a reflection on the advisors, but on the advisory effort itself.

That mission, on the whole, never makes a lot sense except to facilitate the transfer of weapons and treasure to those who are (we hope) our friends today, but will quite possibly become our enemies tomorrow.

Meanwhile, it's another reminder that while other conflicts now take center stage, we remain at war in Afghanistan - nearly 13 years and counting.