A shadowy terror group smuggles a crude nuclear bomb into the United States, then detonates it right in the heart of Washington D.C., setting off a 15 kiloton explosion.

Eighty thousand Americans are killed instantly, including the president, vice president and most of the members of Congress, and more than a hundred thousand more are seriously wounded.

News outlets are soon broadcasting a message they’ve all received from a group claiming responsibility.

It says there are five more bombs hidden in five different cities across the America, and one bomb will be set off each week for the next five weeks unless all American troops based overseas are ordered to immediately return to the U.S. homeland.

The nation is thrown into chaos, as millions scramble to flee the cities, clogging roads and choking telecommunications systems.

The stock market crashes, before trading is halted altogether.

Martial law is declared, amid widespread looting and violence.

That was just one of the nightmare scenarios for a potential nuclear disaster that former U.S. Secretary of Defense William J. Perry vividly described as he delivered the Center for International Security and Cooperation’s annual Drell Lecture on Wednesday.

“My bottom line is that the likelihood of a nuclear catastrophe today is greater than it was during the Cold War,” Perry said.

Most people were “blissfully unaware” of the danger that simmering conflicts in geopolitical flash points around the globe – including Russia, China, North Korea, Iran and Pakistan – could easily turn nuclear, Perry told the Stanford audience.

A new nuclear arms race with Russia

Perry said he had tried to foster closer cooperation between the U.S. and Russia when he headed the Pentagon during the mid ‘90s and helped oversee the joint dismantling of four thousand nuclear weapons.

“When I left the Pentagon, I believed we were well on the way to ending forever that Cold War enmity, but that was not to be,” he said.

William J. Perry shares a video depicting the threat of nuclear terrorism with a Stanford audience.

Since then, relations between the West and Russia have soured badly, prompting Russia to modernize its nuclear arsenal and assume a more aggressive nuclear posture.

“They’re well advanced in rebuilding their Cold War nuclear arsenal, and it is Putin’s stated first priority,” Perry said.

“And they have dropped their former policy of no first use of nuclear weapons, and replaced it with a policy that says nuclear weapons will be their weapon of choice if they are threatened.”

While Perry said he believed Russian president Vladimir Putin did not want to engage in a military conflict with NATO forces, he said he was concerned about the possibility of Russia making a strategic miscalculation and stumbling into a conflict where they might resort to the use of tactical nuclear weapons.

“If they did that there’s no way of predicting or controlling the escalation that would follow thereafter,” Perry said.

Chinese economic problems increasing tensions

In Asia, a slowing Chinese economy could exacerbate domestic political tensions over issues such as wealth inequality and pollution, and encourage Chinese leaders to divert attention from problems at home by focusing on enemies abroad.

“China has had more than 10 percent growth now for almost three decades, but I think there’s trouble ahead,” Perry said.

“The time-proven safety valve for any government that’s in trouble is ultra-nationalism, which in the case of China translates into anti-Americanism and anti-Japanese.”

China has seen a major growth in military expenditures over the last decade, and it has used that investment to build a blue water navy and develop effective anti-ship missiles designed to drive the U.S. Navy hundreds of miles back from the Chinese coastline.

One potential flash point for a conflict between China and the U.S. are the artificial islands that China has been building in the disputed waters of the South China Sea.

“In a sense, China is regarding the South China Sea as a domestic lake, and we regard it and most other countries regard it as international waters, so their actions have been challenged by the U.S. Navy and will continue to be challenged,” Perry said.

North Korea’s growing nuclear threat

Meanwhile, China’s neighbor North Korea has continued to defy the international community and conducted another nuclear test in January.

“North Korea is today building a nuclear arsenal, and I would say clearly it’s of the highest priority in their government, and they have adopted outrageous rhetoric about how they might use those nuclear weapons,” Perry said.

William J. Perry delivers the Drell Lecture in an address entitled "A National Security Walk Around the World."

“These missiles today have only conventional warheads that are of no significant concern, but they are developing nuclear warheads,” Perry said.

“They already have developed a nuclear bomb, and the latest test, as well as tests to come, will be designed to perfect a bomb small enough and compact enough and durable enough to fit into a warhead. If they succeed in doing that, then the bluster will become a real threat.”

Perry said he hoped China and the United States could combine forces and adopt a “carrot and stick” diplomatic approach to force North Korea to abandon its nuclear weapons program – with the United States offering aid and international recognition, and China threatening to cut off supplies of food and aid.

He said he expected to see “more acting out” from the North Korean regime in the coming months, in the form of further nuclear and rocket tests.

Like it or not, the Iran deal is the only deal we’ll get

The landmark deal reached last year, where Iran agree to curtail its nuclear program in exchange for the lifting of economic sanctions, was a better resolution than Perry had expected to the negotiations, but it has met with significant resistance from groups he described as “strange bedfellows.”

“The opposition in Israel and the United States opposed the deal because they fear it will allow Iran to get a bomb,” Perry said.

“Whereas the opposition in Iran opposed the deal because they fear it will prevent Iran from getting a bomb. Both cannot be right.”

Many Republican presidential hopefuls have publicly stated on the campaign trail that they would withdraw from the deal if they got elected to the White House, but Perry said that would be a strategic mistake.

“The opposition in the United States has a simple formula – we should withdraw from the deal, we should reinstate sanctions, and we should renegotiate a better deal,” Perry said.

“Let me be as blunt as I can, this is a pure fantasy. There is not the remotest possibility that the sanction could be reapplied if the United States withdraws from this deal, because the day we withdraw from the deal, our allies are gone, the sanctions are gone, there will be no renegotiations without sanctions, so this deal, like it or not, is the only deal we will ever get.”

Another “Mumbai” attack could spark regional nuclear war

Nuclear rivals India and Pakistan have more than a hundred nuclear weapons on each side, as well as the missiles to deliver them, and a conventional military conflict between them could quickly escalate into a regional nuclear war, Perry said.

Another large-scale terror attack, like the coordinated assault in Mumbai that killed more than 163 people in 2008, could lead India to retaliate militarily against Pakistan (which India blames for encouraging the terror groups operating in Pakistani territory).

Perry said he was concerned that Pakistan would then use tactical nuclear weapons against invading Indian troops, and that India might then respond with a nuclear attack of its own on Pakistan.

“So this is the nightmare scenario of how a regional nuclear war could start,” Perry said.

“A nightmare that would involve literally tens of millions of deaths, along with the possibility of stimulating a nuclear winter that would cause widespread tragedies all over the planet.”

A ray of hope

Despite all the potential for nuclear disaster in the current geopolitical environment, Perry said he was still hopeful that nuclear catastrophe could be avoided.

"While much of my talk today has a doomsday ring to it, that truly is not who I am,” Perry said.

“I’m basically an optimist. When I see a cloud, I look for a ray to shine through that cloud.”

One important step toward reducing the nuclear threat would be improving relations between the U.S. and Russia, he said.

“My ray of sunshine, my hope, is I believe we can still reverse the slide in U.S. Russia relations, he said.

“We must begin that by restoring civil dialog. We must restore cooperation between the United States and Russia in areas where we have mutual interest…If we succeed in doing that, then we can work to stop and reverse the drift to a greater and greater dependence on nuclear weapons.”

Perry ended his speech by urging the audience to keep striving to rid the world of the threat of nuclear weapons.

“We must pursue our ideals in order to keep alive our hope – hope for a safer world for our children and for our grandchildren,” he said.

Stanford nuclear experts said they were skeptical of North Korea’s claim that it had detonated a hydrogen bomb this week.

However, they said the test was an important step forward for North Korea’s nuclear program and would have a destabilizing effect on the entire region.

“I don’t believe it was a real hydrogen bomb, but my greatest concern is not so much whether or not they actually tested a hydrogen bomb, but rather that they tested at all,” said Siegfried Hecker, former director of Los Alamos National Laboratory and senior fellow at Stanford’s Center for International Security and Cooperation.

North Korean dictator Kim Jong-un has “a track record of exaggerated statements, hyperbole and outright lies,” according to Scott Sagan, Caroline S.G. Munro professor of Political Science.

“The propaganda machine in North Korea has made all sorts of claims about Kim Jong-un’s personal prowess and his history, and it is totally unsurprising that he might make exaggerated claims about North Korea’s military prowess,” Sagan said.

Former U.S. Secretary of Defense William J. Perry said he also doubted that North Korea had detonated a two-stage hydrogen bomb.

“Whether it’s a hydrogen bomb or not, it’s very dangerous, destabilizing development,” said Perry.

“It’s obvious they’re working to increase the capability and size of their nuclear arsenal and that represents a huge danger to the region and creates major instability and major concerns on the part of South Korea and Japan.”

Many North Korea watchers had been anticipating another nuclear test.

“We’ve thought that the North Koreans could test at any time – that the tunnels were ready, that they could do this at any time – so it would be a political decision, not a technical decision,” said Thomas Fingar, senior fellow at the Freeman Spogli Institute for International Studies.

Hecker said North Korea’s latest nuclear test would move the country closer to being able to miniaturize a nuclear warhead and mount it on a missile, extending the reach of their nuclear weapons.

“They will have achieved greater sophistication in their bomb design – that is the most worrisome aspect,” Hecker said.

“At this point, what makes their nuclear arsenal more dangerous is not so much explosive power of the bomb, but its size, weight and the ability to deliver it with missiles.”

On the diplomatic agenda, the U.S. and its allies will likely push for stronger sanctions in the wake of the tests, according to Kathleen Stephens, a former U.S. Ambassador to the Republic of Korea and William J. Perry fellow at Walter H. Shorenstein Asia-Pacific Research Center (APARC).

“In the UN the U.S., Japan and South Korea will likely look for another, and stronger, UN Security Council resolution, presumably with some efforts to attach to it some teeth and strengthen sanctions,” Stephens said.

The U.S. Congress is currently considering financial sanctions that would cut of all access to U.S. banks for any banks dealing with the North Koreans.

But financial sanctions would likely be less effective in dealing with North Korea than they had been with Iran, according to Fingar.

“It’s like hitting a masochist,” said Fingar.

“North Korea is relatively insulated from the external economy, where Iran wasn’t. Iran had a middle class, you could make sanctions hurt, they could have a real effect. You could make it hard for the North Koreans to buy luxury goods, but at the end of the day, is that going to bring down the regime?”

Financial sanctions against North Korea could have the unintended consequence of also hurting China, said David Straub, associate director of the Korea program at APARC.

“This could be problematic for China because many of the transactions that North Korea conducts would be going thorough Chinese banks, and the Chinese, understandably might not be happy about the US financial sanctions on them, in effect,” Straub said.

Perry recommended that the U.S. reinvigorate diplomatic talks with North Korea in collaboration with China, South Korea, Japan and Russia.

“I would not give up on negotiations with North Korea yet,” Perry said.

“What could have been done many years ago was following through on negotiations with North Korea at the turn of the Century, which were proceeding robustly in the last years of Clinton’s second term, but were abandoned by the Bush Administration...That was a geo-strategic error.”

But Hecker said those negotiations would be harder now.

“I have previously argued that we should focus on three “No’s” for three “Yes’s” – that is no more bombs, no better bombs (meaning no testing) and no export – in return for addressing the North’s security concerns, its energy shortage and its economic woes,” said Hecker.

“This could have worked when I first proposed it 2008 after one of my seven visits to North Korea. It will be more difficult now."