On April 27th, a veteran Afghan Army pilot (Ahmad Gul) got into an argument with nine American pilot trainers (all of them military, although one was retired military working as a civilian contractor). The Afghan pulled his weapon, disarmed the nine then shot all of them dead. Gul then killed himself. While the Taliban took credit, kin of the killer said that there was no Taliban connection to Gul, and that the main cause was family and financial problems, and inability to deal with all the stress. The 50 year old Gul had served in the Afghan military for twenty years (before and after the Taliban ran the government). He had a lot to be stressed about. He was not alone. This was the seventh time that Afghan troops or police (or Taliban impersonating them) have shot and killed foreign troops.
Unfortunately, this sort of violence is common in Afghanistan. It is a warrior culture, and settling disputes with violence is much more common than in the West. There is also a lot more domestic violence, with medical aid workers shocked at the number of injured wives and children they are called on to treat. But there are also a lot of men with wounds, and a lot who suddenly disappear (local customs calls for burial within 24 hours of death). Even without the Taliban related violence, the murder rate is several times higher than found in the West.
For example, the murder rate in the Western hemisphere (about 8 per 100,000 people a year) is much higher than in Europe, where it is about 3-4. That is another example of the "frontier culture" effect. Middle Eastern nations have rates of between 5-10. The United States rate is about six per 100,000. There are other parts of the world that are more violent. Iraq has a murder rate in the 20s. That's not a lot higher than it was under Saddam (10-20 a year), but less than a third of what it was several years ago. In Africa, especially Congo, Sudan and South Africa, you find similar murder rates. Only South Africa has a sufficiently effective government to actually keep accurate track of the murder rate, mostly from crime, but it's over 50 per 100,000. It's worse in places like Congo and Sudan, but the numbers there are only estimates by peacekeepers and relief workers. In southern Thailand, a terror campaign by Islamic radicals has caused a death rate of over 80 per 100,000. Historians have been able to find similar patterns of deadly violence in Medieval Europe (in those places where large quantities of church records, that track births and deaths, survived).
Afghanistan is a violent place, and always has been. The problem is that the continual violence makes it difficult to put the current fighting against the Taliban into context. The country has long been awash in weapons, and men eager to use them. Afghans has been known as good recruits for local conquerors for thousands of years. The several major invasions of India over the last thousand years saw lots of Afghans in the ranks of the conquering armies. In some cases, there were so many Afghans, that Indian records simply record the invaders as "Afghans."
When not invading neighbors, Afghans practice on each other. Not a lot of accurate record keeping out there in the bush, but public health stats indicate an average life span in the 40s. There's a lot of disease, accidents, and not much modern medicine. But there's also much talk of murder. There are tribal feuds, lots of banditry, and even within families, there are murders and executions. The problem with tribal cultures is the difficulty controlling this kind of violence. In much of Afghanistan, it isn't being controlled and, as always, the resulting deaths are not being reported either. Thus the civilian murder rate, excluding the Taliban, is probably over 10 per 100,000 year. Many of the Taliban related deaths would have occurred anyway, because the Taliban are basically a tribal rebellion by some of the Pushtun tribes that want to run the country (in the name of God, of course, as it has long been good PR to commit your atrocities while invoking a higher power.)
The Taliban, according to their public announcements, feel that they could quickly overcome the other tribes and take control, were it not for the 150,000 foreign troops in the country. That's recognition that most of the Taliban losses are at the hands of foreign troops. But it also implies that the Taliban feel they have access to plenty of people who know how to kill and, if not interfered with, can butcher enough Afghans to gain control of a nation of 25 million people.