SINCE the end of the cold war one simple geopolitical rule has endured: do not take on America. The country’s armed forces have been so well resourced and so technologically superior that it would be utterly foolish for any state to mount a direct challenge to the superpower or its allies. This rule still holds—but it is no longer quite as compelling as it once was. Although America still possesses by far the most capable armed forces in the world, the technological advantage that guarantees it can defeat any conceivable adversary is eroding rapidly.
“We are entering an era where American dominance on the seas, in the skies, and in space—not to mention cyberspace—can no longer be taken for granted,” admitted Chuck Hagel, the outgoing secretary of defence, last year. He argued that America urgently needed to develop a new generation of military technologies, lest another country come to feel capable of challenging it. His warning was timely.