In October 2002, Barack Obama, then an obscure state senator in Illinois, stood in Federal Plaza in Chicago and gave a speech about Iraq that launched his career toward the White House.

“I don’t oppose all wars,” Obama told the crowd. “What I am opposed to is a dumb war.”

More than a decade later, Obama’s vision of a smart war — or at least a new way of war — is clear, even if he has not publicly articulated it. He has presided over a vast expansion of CIA and Pentagon authorities to secretly kill thousands of people around the globe, relying on missile-firing drone aircraft, special operations teams, mercenaries and privateers.

History will decide whether Obama championed a counter-terrorism policy that contained a national threat at low cost and little risk — or if he authorized targeted killings (critics call them extra-judicial executions) on such a sanguinary scale that America made more enemies than it eliminated.

In The Way of the Knife, Mark Mazzetti pulls back some of the veils from America’s ongoing shadow wars in Pakistan, Yemen, Somalia and elsewhere. The full story probably won’t emerge for years, and this often colorful account raises as many questions as it answers. But Mazzetti finds new details and tracks the ominous blurring of traditional roles between soldiers and spies, the lush growth of a military-intelligence complex, and what the shift portends for the future.

Mazzetti covers national security at The New York Times, where he regularly breaks scoops. For his first book, he seems to have emptied his notebooks of nuggets — a U.S. drone strike in the Philippines, an eavesdropping device called “typhoon box,” a failed military operation code-named “celestial balance” in Somalia — in a sometimes jumpy narrative. But it is a valuable addition to a canon that is exposing America’s use of lethal operations far from declared war zones.

The history, at least, is familiar. The CIA had run into a political buzz saw in the early 1970s for harebrained assassination plots — one involved giving Fidel Castro an exploding cigar — and again after the Iran-Contra mess in the 1980s. People were hauled before congressional committees and convicted at criminal trials. After that, especially with the fall of the Soviet Union, the CIA largely abandoned sabotage, coups and paramilitary operations and focused instead on stealing secrets from foreign governments, the traditional role of an espionage agency.

But soon after the terrorist attacks of Sept. 11, 2001, the CIA was killing dozens of people in Afghanistan with a weapon tested for the first time only six months earlier: a Predator drone armed with a Hellfire missile. It was the perfect weapon for a spy service: It killed from afar, usually out of public view and without accountability. It was the start of remote-controlled war (although not “killer robots,” as Mazzetti incorrectly writes), the policy that Obama ultimately embraced.

With the dawn of the drone age, the CIA got a license to kill. Since then, the author warns, it has become “a killing machine, an organization consumed with man hunting.” The CIA director has become a “military commander running a clandestine global war with … very little oversight.” It is the “willing executioner of America’s enemies.” It has “gone on a killing spree.” And so on.