"A decade of war is now ending," U.S. President Barack Obama proclaimed in his second inaugural address.

But war is not ending, it is changing — and has been for years. Obama has cut back on heavy-footprint, conventional-force war in two countries. At the same time, he has presided over the rise of a secret, nimbler war defined by covert action, Special Forces, drone surveillance and targeting, cyber attacks and other stealthy means deployed in many countries. This new form of warfare needs a firmer political and legal foundation.

Signs of the new war are all around us. Last week a Justice Department "white paper" outlining the president's power to kill U.S. citizens associated with al-Qaida was leaked to the public. Since the beginning of the year, U.S. drone attacks in Pakistan and Yemen have killed dozens of terrorists, and the government is planning a drone base in North Africa to surveil, and perhaps later attack, Islamist militants in the region. We have also recently learned that the Pentagon is ramping up its offensive cyber-capabilities and that government lawyers have secretly concluded that the president has "broad power" to order preemptive cyber strikes.