If the period from Hiroshima to the end of the Cold War can be called the first atomic age, today’s headlines show we’ve entered a new period, the age of proliferation. Nuclear powers India and Pakistan square off across a disputed border. North Korea’s stockpile continues to grow. Iran makes clear its nuclear ambitions, while those of Saddam Hussein are heatedly debated. And then there is the threat of nuclear-armed terrorists.

Two new books on the history of the first atomic age shed light on the prospects of this new one. Despite their shortcomings, they raise once again important issues of diplomacy, deterrence, and preemption in the age of proliferation.

Certainly, there were bombs before Hiroshima, writes Gerard DeGroot in “The Bomb” (Harvard University Press, 397 pages, $27.95). But it is only since August 6, 1945, that we have been able to speak about “The Bomb” without having to elaborate further.

The origin of the bomb goes back to the start of the 20th century and the nascent revolution in physics. In 1904 British physicist Frederick Soddy noted that the atom could be tapped as a source for energy, but his insight barely caused a ripple. Until the 1930s, writes Mr. DeGroot, physicists were perceived as nearly the least likely to change the world. They were luftmenschen – airheads riding on light beams.

The upheaval of the 1930s and World War II changed that. Science became the handmaiden of war and the bomb took shape in the minds of Jewish scientists fleeing Hitler. While Albert Einstein is often cast as being instrumental in the effort to develop the bomb, the credit belongs to fellow refugee scientist Leo Szilard, who drafted the letter to FDR, which Einstein merely signed. Einstein doubted the feasibility of the weapon, and had he known the Germans were not pursuing one, he would not have lent his stature to the proposal.

At a cost of $2 billion, the Manhattan Project was more than just an industrial/scientific experiment; it was a social one, too. Overnight, the population of Los Alamos almost quadrupled, spawning its own baby boom, with nearly 1,000 born between 1943 and 1949!

Mr. DeGroot paints a lively picture of the Manhattan Project (an innocuous name, meant to throw off German spies), bringing to life such figures as Oppenheimer – a genius who, according to colleagues, “couldn’t run a hamburger stand.” While elements of this story have appeared before in such books as Richard Rhodes’s “Dark Sun: The Making of the Atomic Bomb,” Mr. DeGroot’s tale is gripping. The scientific recruits were young, drawn to the project out of patriotism and a chance to be on the cutting edge.

Recounting the Soviet effort to catch up with America and the testing of ever more powerful bombs, Mr. DeGroot captures the hysteria and absurdity of the Cold War era. He tells how Hans Bethe’s criticism of the decision to build the H-bomb in Scientific American resulted in thousand of copies of the magazine being confiscated and destroyed for disclosing “secrets.” He also tells how the bomb evolved into a kind of national fashion accessory – a cheap way to flaunt status.

Mr. DeGroot follows the bomb through the reckless years of 1950s and 1960s – with their nonstop crises: the U2 spy plane, Berlin, the Cuban missile crisis – to its “midlife crisis” in the 1970s and finally to the current fear of weapons falling into the hands of terrorists. In 1964, writes Mr. DeGroot, the U.S. conducted a secret study to find out how hard it would be for an amateur to build a bomb. The answer: not hard at all. And today it’s even easier, given the impoverished state of Russia’s nuclear program.

To date, the attempt to head off this looming crisis has yielded pathetic results: In 2003, the United States and Russia established the Nuclear Cities initiative to create jobs for unemployed nuclear scientists. Two years later 100 jobs had been created. Some 60 years after the Manhattan Project and $5.8 trillion later, we are no safer than we were in 1945 – in fact, the danger may be greater. In the age of proliferation, deterrence is dead.

“The Worlds of Herman Kahn: The Intuitive Science of Thermonuclear War” by Sharon Ghamari-Tabrizi (Harvard University Press, 374 pages, $26.95) picks up where “The Bomb” leaves off – or perhaps it would be more accurate to say that Ms. Ghamari-Tabrizi, an independent scholar, explores areas Mr. DeGroot does not pursue. Her topic is the struggle between the military and the civilian analysts for dominance over postwar nuclear strategy.

Considered the inspiration for Stanley Kubrick’s “Dr. Strangelove,” nuclear strategist Herman Kahn (1922-83) was a notorious figure in the 1960s. A mathematician and a physicist, this 350-pound thinker worked at the Rand Corp. from the late 1940s until 1961, when he founded the Hudson Institute. A series of lectures on nuclear strategy that Kahn gave while still at Rand led to “On Thermonuclear War,” an analysis of nuclear strategy that argued the United States could win the next war, and that the survivors would cope – and, ultimately, thrive. Where others saw a subway system, Kahn saw a nodal system of bomb shelters.

Ms. Ghamari-Tabrizi employs an interdisciplinary approach that cuts across historical, sociological, technological, and cultural lines. Ranging from high- to lowbrow, she seeks to place Kahn in the context of his times. But in doing so, she loses sight of Kahn himself.

She seems to find Kahn a repellant figure, intellectually and physically, but she also has been taken in by what is peripheral to Kahn rather than what is central to his thought. In her description and understanding of the Cold War era, the entire Cold War congeals into the witch-hunts of McCarthy and the House of Un-American Activities Committee. Gone is the Soviet brutality in Hungary in 1956 or Bela Kuns in Czechoslovakia or the Berlin Crisis.

The pity is that Ms. Ghamari-Tabrizi is on to something. Kahn was one of the first in a long line of civilian strategic thinkers who tried to think the unthinkable and to quantify the unquantifiable. At the heart of this book is the contention by system analysts like Kahn that systems analysis, or simulation, was superior to first-hand knowledge and that the scenarios offered practical insights. This has been an ongoing struggle, and can still be seen in the recent skirmishing between Defense Secretary Donald Rumsfeld and the Chiefs of Staff.

Needless to say, September 11 colors Ms. Ghamari-Tabrizi’s book, as it does everything in the age of proliferation. Strategists are being challenged to dream up ever more inventive threats and scenarios. Had Ms. Ghamari-Tabrizi approached Kahn’s life and thought with less hysteria and with greater detachment, her book might serve as an important bridge between the first atomic age and the new one. To be sure, our enemies are casting a much cooler, more calculated eye on the opportunities now available to them.