Russia's latest "Zapad" military exercise just took place on NATO's eastern border. Tens of thousands of soldiers participated in the massive four-yearly war games that are both a drill as well as a show of strength for the West. Next time around, in 2021, those troops might be sharing their battle space with a different type of force: self-driving drones, tanks, ships and submersibles.

Drone warfare is hardly new — the first lethal attack conducted by an American unmanned aerial vehicle took place in Afghanistan in October 2001. What is now changing fast, however, is the ability of such unmanned systems to operate without a guiding human hand.

That's a truly revolutionary shift — and one every major nation wants to lead. Critics have long feared countries might be more willing to go to war with unmanned systems. Now, some see a very real risk that control might pass beyond human beings altogether.