What was a science-fiction scenario not much more than a decade ago has become today’s news. In Iraq and Afghanistan, military drones have become a routine part of the arsenal. In Pakistan, according to American officials, strikes from Predators and Reapers operated by the C.I.A. have killed more than 2,000 militants; the number of civilian casualties is hotly debated. In Yemen last month, an American citizen was, for the first time, the intended target of a drone strike, as Anwar al-Awlaki, the Qaeda propagandist and plotter, was killed along with a second American, Samir Khan.

If China, for instance, sends killer drones into Kazakhstan to hunt minority Uighur Muslims it accuses of plotting terrorism, what will the United States say? What if India uses remotely controlled craft to hit terrorism suspects in Kashmir, or Russia sends drones after militants in the Caucasus? American officials who protest will likely find their own example thrown back at them.

“The problem is that we’re creating an international norm” — asserting the right to strike preemptively against those we suspect of planning attacks, argues Dennis M. Gormley, a senior research fellow at the University of Pittsburgh and author of “Missile Contagion,” who has called for tougher export controls on American drone technology. “The copycatting is what I worry about most.”

The qualities that have made lethal drones so attractive to the Obama administration for counterterrorism appeal to many countries and, conceivably, to terrorist groups: a capacity for leisurely surveillance and precise strikes, modest cost, and most important, no danger to the operator, who may sit in safety thousands of miles from the target.

Image Credit... Guy Billout

To date, only the United States, Israel (against Hezbollah in Lebanon and Hamas in Gaza) and Britain (in Afghanistan) are known to have used drones for strikes. But American defense analysts count more than 50 countries that have built or bought unmanned aerial vehicles, or U.A.V.’s, and the number is rising every month. Most are designed for surveillance, but as the United States has found, adding missiles or bombs is hardly a technical challenge.