Famed detective Sherlock Holmes once solved a case based on the fact that a dog didn’t bark. In our time, nuclear weapons are the equivalent of that silent pooch.

At a recent speech in Prague, President Barack Obama declared that, “As the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act,” to eliminate nuclear weapons. “We cannot succeed in this endeavor alone, but we can lead it,” he added.

But this view ignores decades of military history, and fails to give the U.S. the credit it deserves.

Never before in history had a country or group developed an overwhelming weapon -- then declined to use it. When British forces met lesser-armed dervish fighters at the battle of Omdurman in 1898, for example, they unapologetically used machine guns to mow down 10,000 attackers while losing fewer than 50. “Whatever happens, we have got/The Maxim gun, and they have not,” observed Hilaire Belloc.

Later, World War I brought great leaps in weapons technology. And no matter how awful weapons such as poison gas were, both sides eagerly deployed them as soon as possible.

Sometimes even too quickly. The British invented tanks, but by rolling them out piecemeal instead of in massed formations, they often wasted their technological advantage. Decades later it was the Germans who conquered a continent with effective tank warfare.

But against that backdrop, consider “the bomb.”

Americans, knowing they were in a race for the future of humanity, scrambled to split the atom and unleash its overwhelming power during World War II. Pre-war Germany had led the world in nuclear physics. But by running off his country’s Jewish scientists Hitler had, luckily, squandered that advantage. Shortly after Germany surrendered in 1945, the U.S. developed atomic weapons.

In August, the U.S. military used nuclear bombs to destroy Hiroshima and Nagasaki, causing Japan to surrender. The death toll was unprecedented. Some 140,000 people in Hiroshima and 80,000 in Nagasaki were killed almost immediately by just two bombs. Still, these numbers pale next to the number of fatalities an all-out invasion could have caused.

A study produced by the Secretary of War estimated that between 1.7 and 4 million Americans could have been casualties, including 400,000 to 800,000 killed. Meanwhile some 5 to 10 million Japanese -- many if not most of them civilians -- could have been killed.

And this is the point President Obama apparently misses: Having developed nuclear weapons and used them to end the greatest military conflict in history, the United States never used them again. Talk about showing moral leadership.

We almost take it for granted today that, as military theorist Thomas P.M. Barnett has observed, no country with nuclear weapons is going to be allowed use them. That’s why South Africa gave up its nuclear program, and why advanced nations such as Japan don’t bother having atomic weapons. If there’s a dispute over the Chunnel, for example, France isn’t going to nuke London.

But for decades, humans assumed that nuclear war was inevitable. In 1962 novelist Arthur Hailey, himself a British pilot in W.W. II, wrote “In High Places,” a book that featured a world where Canada and the U.S. had to merge their sovereignty to survive an impending Soviet nuclear attack.

The reason no other nation ever used atomic weapons is because the U.S. voluntarily put its on the shelf, even though that cost American lives. Tens of thousands of Americans were killed in Korea, yet the U.S. didn’t use nuclear bombs to stop invading Chinese troops. Vietnam dragged on for years, yet the U.S. never considered dropping nuclear weapons on Hanoi. The Soviets could have used nukes in Afghanistan, but didn’t. That’s probably because the U.S. hadn’t used them in its limited wars.

Of course, after 60-some years, the picture is changing. In the years ahead it won’t be merely stable nation-states that will have nuclear weapons. Unstable -- possibly suicidal -- regimes in Iran and North Korea likely will have them as well.

The U.S. has shown great leadership in this area as well, of course. Washington has attempted to work with international organizations to slow the proliferation of nuclear arms. And the U.S. has designed and built the first effective missile-defense systems, technology it’s eager to share with allies so they’ll be able to protect themselves from a nuclear North Korea or Iran.

Nuclear weapons haven’t barked because American leadership kept them muzzled. That’s the sort of “leadership” we’ve exhibited for decades, and will continue to feature in the years ahead, whether we get credit for it or not.