As the gap has grown between Washington’s global reach and its shrinking mailed fist, as it struggles to maintain 40% of world armaments (the 2012 figure) with only 23% of global gross economic output, the U.S. will need to find new ways to exercise its power far more economically. As the Cold War took off, a heavy-metal U.S. military — with 500 bases worldwide circa 1950 — was sustainable because the country controlled some 50% of the global gross product.

But as its share of world output falls — to an estimated 17% by 2016 — and its social welfare costs climb relentlessly from 4% of gross domestic product in 2010 to a projected 18% by 2050, cost-cutting becomes imperative if Washington is to survive as anything like the planet’s “sole superpower.” Compared to the $3 trillion cost of the U.S. invasion and occupation of Iraq, the NSA’s 2012 budget of just $11 billion for worldwide surveillance and cyberwarfare looks like cost saving the Pentagon can ill-afford to forego...

Surveillance of foreign leaders provides world powers — Britain then, America now — with critical information for the exercise of global hegemony. Such spying gave special penetrating power to the imperial gaze, to that sense of superiority necessary for dominion over others. It also provided operational information on dissidents who might need to be countered with covert action or military force; political and economic intelligence so useful for getting the jump on allies in negotiations of all sorts; and, perhaps most important of all, scurrilous information about the derelictions of leaders useful in coercing their compliance.