MUNICH – At the World Economic Forum’s recent annual meeting in Davos, I participated in a panel of defense leaders to discuss the future of the military. The issue we addressed is a critical one: What kind of war should militaries today be preparing to fight?

Governments have a very poor track record when it comes to answering this question. After the Vietnam War, for example, the United States’ armed forces suppressed what it had learned about counter-insurgency, only to rediscover it the hard way in Iraq and Afghanistan.

America’s military interventions in these countries exemplify another key challenge of modern warfare. As outgoing US Secretary of Defense Chuck Hagel pointed out in a recent interview, in war, "things can get out of control, and drift and wander” in ways that can cause a military to fall into a more "accelerated” use of force than was initially anticipated. Against this background, the notion that force alone can transform conflict-riven societies in the Middle East and elsewhere is a dangerous fallacy.

But, while war and force may be down, they are not out. They are simply evolving according to a new "generation” of rules and tactics.

The first generation of modern warfare comprised battles fought with massed manpower, using Napoleonic line and column formations. The second, which culminated in World War I, was driven by massed firepower, and is expressed in the saying, reportedly coined at the Battle of Verdun in 1916, "artillery conquers, infantry occupies.” And the third generation – perfected by Germany with the "blitzkrieg” method employed in World War II – emphasized maneuver over force, with militaries using infiltration to bypass the enemy and collapse its force from the rear, rather than attacking frontally.

Fourth-generation warfare takes this decentralized approach one step further, with no definable fronts at all. Instead, it focuses on the enemy’s society, reaching deep into its territory to destroy political will. One might even add a fifth generation, in which technologies like drones and offensive cyber tactics allow soldiers to remain a continent away from their civilian targets.

While particular generational delineations are somewhat arbitrary, they reflect an important trend: the blurring of the military front and the civilian rear. Accelerating this shift is the replacement of interstate war by armed conflict involving non-state actors such as insurgent groups, terrorist networks, militias, and criminal organizations.

Confusing matters further is the overlap among these groups, with some even receiving state support. The Revolutionary Armed Forces of Colombia – Latin America’s oldest guerilla group – formed alliances with narcotics cartels. Some Taliban groups in Afghanistan and elsewhere developed close ties with transnational Al Qaeda terrorists. The insurgents in eastern Ukraine are fighting alongside Russian troops (bearing no insignias).

Such organizations often take advantage of states that lack the legitimacy or capacity to administer their own territory effectively, launching a mix of political and armed operations that, over time, give them coercive control over local populations. The result is what General Sir Rupert Smith, a former British commander in Northern Ireland and the Balkans, called "war among the people” – a kind of struggle that is rarely decided on conventional battlefields by traditional armies.

These hybrid wars are fought using a wide variety of weapons – not all of which have firepower.

With cameras in every cell phone and photo-editing software on every computer – not to mention the prevalence of social media – the information contest has become a critical aspect of modern warfare, exemplified in the current wars in Syria and Ukraine.

In hybrid warfare, conventional and unconventional forces, combatants and civilians, physical destruction and information manipulation become thoroughly intertwined. In Lebanon in 2006, Hezbollah fought Israel through well-trained cells that combined propaganda, conventional military tactics, and rockets launched from densely populated civilian areas, achieving what many in the region considered a political victory. More recently, Hamas and Israel have conducted air and land operations in the densely populated Gaza Strip.

This kind of warfare emerged largely in response to America’s overwhelming conventional military advantage after the Soviet Union’s collapse, underscored by its victory in the 1991 Iraq War, with only 148 American casualties, and its intervention in the 1999 conflict in Kosovo, in which no American lives were lost. In the face of this asymmetry, America’s opponents – both state and non-state actors – began to emphasize unconventional tactics.

In China, for example, military planners developed a strategy of "unrestricted warfare” that combines electronic, diplomatic, cyber, terrorist-proxy, economic, and propaganda tools to deceive and exhaust US systems. As one Chinese military official put it, "the first rule of unrestricted warfare is that there are no rules.”

For their part, terrorist groups, recognizing that they cannot defeat a conventional military in a direct war, attempt to use governments’ own power against them. With violent theatrics, Osama bin Laden outraged and provoked the US, driving it to overreact in ways that destroyed its credibility, weakened its alliances in the Muslim world, and ultimately exhausted its military – and, in a sense, its society.

The Islamic State is now employing a similar strategy, mixing ruthless military operations with an incendiary social-media campaign, punctuated by photos and videos of brutal executions, including the beheading of US and other Western citizens. These efforts have mobilized the Islamic State’s enemies, while inspiring a growing number of discontented individuals and groups to self-recruit to its banner.

The unpredictable evolution of warfare poses a serious challenge for defense planners. For some weak states, internal threats provide clear objectives. The US, for its part, must balance continued support for its conventional military forces, which remain an important deterrent in Asia and Europe, with investment in a broad portfolio of alternative capabilities that conflicts in the Middle East require. At a time of unprecedented change, the US – and other major powers – must be ready for anything.

Joseph S. Nye, a former US assistant secretary of defense and chairman of the US National Intelligence Council.

Copyright: project syndicate