The greatest change ever in the defence policy and military strategy of the North Atlantic Treaty Organisation occurred in 2014 in response to a series of major cyber attacks against NATO member states and partner states - Estonia in 2007, the United States and Georgia in 2008, and others in later years - and to a general transformation of the security environment in which cyberwar and other threats to cybersecurity gain rapidly in importance. At the 2014 Wales Summit, NATO recognised that cyber defence is part of its central task of collective defence and that Article 5 of the North Atlantic Treaty - ”The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all . . .” - can be invoked in the case of cyber attacks. This statement is the first and only expansion of the meaning of Article 5 and the first and only addition of a new type of warfare to the policy and strategy of NATO. After the change, the Alliance must face new challenges not less urgent and difficult than the old ones of kinetic warfare or weapons of mass destruction. This article addresses the broadest strategic context of the change. An analysis is made in the light of the global strategic thought and of the development of warfare through history. By entering the new strategic space of cyber warfare, NATO proves itself to be among the world’s most modern and advanced powers while, at the same time, it returns to the ancient - and lasting - tenet of strategy: information is not inferior to force. This way the Alliance moves away from Carl von Clausewitz and closer to Sun Zi. The recognition of cyberspace as a strategic space also corresponds to another influential idea in the heritage of strategy: the concept of the ”great common” the control of which is the key to the power over the world and over war and peace worldwide. Alfred Thayer Mahan considered the global ocean to be the ”great common” crossed by vital trade routes and by navies competing for superiority. Now cyberspace is as open, vital and fragile as the maritime space was in Mahan’s vision. Cyberwar also creates a promise and a temptation of a decisive strike - the first and last strike in a war - circumventing all military defences and paralysing the enemy country. It is a new version - less lethal or not, dependent on the tactics of cyber attacks in a cyber offensive - of the idea of strategic bombing and of the entire concept of air power, especially by its visionary Giulio Douhet, and then of nuclear strategy. Finally, the article provides two practical recommendations regarding the policy and structure of the North Atlantic Alliance in unfolding new era. Now NATO needs a speedy follow-on to the breakthrough decision of the Wales Summit. Cyber defence should be fully integrated into the next Strategic Concept which is expected in or around 2020 but could be worked out sooner because of the accelerating transition of the security environment. NATO should also consider establishing a global Cyber Command to maintain the initiative and to assure the credibility of the enlarged meaning of Article 5 of the North Atlantic Treaty. This credibility will be immediately, continuously and comprehensively tested by many players of the global game.