Adm. James Stavridis was supreme allied commander at NATO from 2009 to 2013 and head of U.S. Southern Command in Miami from 2006 to 2009. He is to become dean of the Fletcher School at Tufts University this summer.

I am often asked what keeps me awake at night after nearly 40 years as a Navy officer, including four years as supreme allied commander for global operations at NATO. There is no shortage of frightening issues: Iran, North Korea, the insurgency in Afghanistan, civil war in Syria , cyberthreats , chemical weapons, terrorism.

But my one-word answer may surprise: convergence.

Convergence may be thought of as the dark side of globalization. It is the merger of a wide variety of mobile human activities, each of which is individually dangerous and whose sum represents a far greater threat.

The most obvious example of this kind of convergence is narco-terrorism. Drug cartels use sophisticated trafficking routes to move huge amounts of heroin, cocaine and methamphetamines. Terrorists can in effect “rent” these routes by co-opting the drug cartels through money, coercion or ideological persuasion. These organizations can then move personnel, cash or arms — possibly even a weapon of mass destruction— clandestinely to the United States.

Other globally trafficked illicit goods can also be found constantly moving on these routes: stolen and counterfeit intellectual property, illegal migrants, human slaves, laundered cash, sophisticated armaments. Meanwhile, in laboratories in North Korea, Iran and Syria, sophisticated weapons of mass destruction are in production or being researched. When global trafficking routes and weapons of mass destruction merge, the result will be catastrophic.

A special case of this kind of convergence is emerging in the cyberworld, where the greatest mismatch between the level of threat to our country (high) and our level of preparation (low) is evident. High-threat packages move through the world’s servers, fiber-optic cables and routers in the service of nations, anarchic organizations and garden-variety hackers. Trillions of dollars’ worth of cybercrime occurs each year; if the cyber-capability and the resultant cash converge with terrorist groups or pariah states such as Iran and North Korea, the potential for catastrophe is high.

So, what can be done? First and foremost, the United States and the international community must recognize the threat this kind of deviant globalization poses. Convergence of these mobile illicit activities can rapidly undermine global security norms. Too often the focus is on single-point threats — drugs, money laundering, human trafficking, weapons trading, production of weapons of mass destruction — while the true threat lies in their convergence. The Obama administration’s Strategy to Combat Transnational Organized Crime, published in 2011, is a step in the right direction.

Second, we must recognize that it takes a network to confront another network. Networks of criminal and terrorist activities are converging. The United States needs to build its own network solutions. This means combining international, interagency, and private and public mechanisms for cooperation — or open-source security — across the spectrum of threat. Cyberthreats cannot be dealt with in isolation; combating them requires full cooperation of the private sector; linkages among the Defense, State, Commerce, Homeland Security and Justice departments; and international partners, beginning with NATO.

Third, we must follow the money. Huge sums of cash from these trafficking activities finance terrorists and insurgents such as the Taliban, as well as corruption. The money is used to undermine fragile democracies. Efforts to upend threat financing must be fused with international initiatives, move across U.S. agency lines and have the cooperation of the private-sector institutions involved.

Fourth, we must shape and win the narrative. Many have said there is a “war of ideas.” That is not quite the right description. Rather, the United States is a “marketplace of ideas.” Our ideas are sound: democracy, liberty, freedom of speech and religion — all the values of the Enlightenment. They have a critical role in confronting the ideological underpinnings of crime and terror. Our strategic communications efforts are an important part of keeping our networks aligned and cohesive.

Fifth, we must sort out the balance between civilian and military activity in areas such as counter-narcotics and cyberspace. Legal complexities, such as issues of privacy and jurisdictional questions, need to be addressed. But the bottom line is that both have a role: Witness the cooperation between the Drug Enforcement Administration and the Defense Department, whose interagency operations in Latin America and the Caribbean have led to the capture of narco-terrorists.

Just over a century ago , the poet Thomas Hardy wrote “The Convergence of the Twain” about the collision of the Titanic and the iceberg that sank it. “And as the smart ship grew/ In stature, grace, and hue/ In shadowy silent distance grew the Iceberg too.” There is an iceberg out there in the form of weapons of mass destruction; what is most worrisome is the convergence of such a weapon with a sophisticated global trafficking route enabled by cybercrime and the cash it generates. That is the convergence we must do all in our power to prevent.