Editor's note: Peter Bergen is CNN's national security analyst, a director at the New America Foundation and the author of "Manhunt: The Ten-Year Search for bin Laden -- From 9/11 to Abbottabad." Emily Schneider is a research associate at the New America Foundation.
(CNN) -- Over this past weekend, Hezbollah, the militant Shiite group that is headquartered in Lebanon, reportedly used drones to bomb a building used by the al Qaeda affiliated Nusra Front, along Lebanon's border with Syria.
The armed drones, combined with fire from Hezbollah ground troops, killed 23 Nusra Front militants and wounded some 10 others, according to a report by an Iranian news agency.
Iran is the key sponsor for Hezbollah and has plausibly claimed for the past several years to have succeeded in manufacturing armed drones.
Hezbollah's use of drones marks a milestone for terrorist groups worldwide: It would be the first time a group other than a nation state used armed drones successfully to carry out an attack, marking an important step towards closing the gap between the technological capabilities of countries such as the United States and militant groups such as Hezbollah.
After all, it was only in the months immediately after 9/11 that the United States mastered the technology of arming drones and began to use them in combat.
Now, 13 years later a militant organization appears to have reached the same milestone.
Previously, drones were known to have been used by militant groups only for surveillance purposes. Last month, ISIS uploaded a video to YouTube that showed aerial views of Syrian Army Military Base 93 in Raqqa province in northern Syria that had purportedly been shot by a drone.
Libyan opposition fighters targeting Libyan dictator Moammar Gadhafi used sophisticated drones for surveillance in the summer of 2011.
Hezbollah had used drones for surveillance before, but the drones were used on Lebanon's border with Israel. In April, the Israeli military said it had shot down a drone off the coast of Haifa and that Hezbollah operated it. Although Hezbollah denied responsibility for that drone, it did claim that it had operated another drone that flew 35 miles into Israel in October.
If Hezbollah does indeed have armed drones, it joins an elite group of nations: Only the United States, United Kingdom, and Israel and are known to have deployed armed drones in combat.
According to a count by New America, some 80 countries have some kind of drone capability -- but few of them have succeeded in arming their drones.
Russia, China, and Iran possess armed drones but have yet to use them in combat.
Hezbollah's use of drones to target another militant group shows how warfare is changing: The monopoly of states on the use of military force is eroding, and new technology is leveling the playing field between states and militant groups.
So what can the United States and other nations do to protect themselves from this dawning threat? It's a subject, of course, of great interest in Israel where accounts of Hezbollah's drone strike on the Nusra target over the weekend were all over Israeli media during the past 24 hours.
Most armed drones are relatively easy to shoot down if you have a sophisticated air defenses or a fleet of jet fighter aircraft. Western countries generally have these, but one can imagine a dystopian future where terrorist groups are able to deploy armed drones against less well defended targets.
Indeed, that future may have already arrived.