How Would Clausewitz See Modern War?

Prussian general Carl von Clausewitz’s insight into the essence of war has held since the dawn of civilization when Stone Age man wielded clubs and spears. As Clausewitz taught in On War in the 19^th century, “War is . . . an act of force to compel our enemy to do our will.” That “is the object of war.” 

The specific aims were security, glory, booty, or hegemony—even nubile women, to recall what the Romans did to the Sabines in their quest for wives.

Yet the means and ways are ever changing, and they would stump the Master in our day: insurgencies, internal wars between factions and ethnicities, states vs. non-states like Hamas and Hezbollah, an endless succession of proxy wars. To highlight the stark contrast between then and now, a quick survey of modernity prior to the 21^st century may pierce the historical fog. The review reveals three emblematic faces of war preceding the present. It can help us to understand warfare in the here and now.

1. The “real” first world war, 1618–48:
The Thirty Years’ War raged across Europe (the main arena), Africa, and the Caribbean on land and sea. It was unconstrained violence, the bloodiest melee ever involving regular troops, marauding bands, and privateers. It killed an estimated four to eight million soldiers and civilians, wiping out one-third of Central Europe’s population. As Robert O’Connell tells in Of Arms and Men(1990), “Armies increasingly devoid of intelligible political objectives . . . degenerated into traveling armed mobs living in a symbiotic relationship with the countryside.”

The carnage came “cheap.” Mercenaries and fortune seekers did not have to depend on long supply lines for their sustenance. They lived off the hapless, robbing them of food and using torture to extract hidden assets.  

2. Limited war in the 18^th century:
In this period, the stage was radically transformed. Expensive to equip and train, highly disciplined professional forces drained the coffers of potentates, straining their sparse taxing powers. Prussia’s Frederick the Great depended on British subsidies in his Seven Years’ War of 1756–63. In turn, the Redcoats courted bankruptcy in the coterminous French and Indian War in North America. Hence the built-in limits on violence, with maneuvering and sieges trumping large-scale battles.

A British commander wrote in 1711, “If any misfortune should occur . . . it would be impossible to get our troops recruited again next year.” Thirty-seven years later, another commander was told to “preserve your army” and not “to run a risk.” Frederick the Great quipped that some wars were like “a card-game between two friends.” 

As historian Jeremy Black notes, compared to the slaughter of 1618–48, the 18^th century was a heaven of sorts—lots of wars, but restricted in scope and bloodshed. Custom allowed commanders to capitulate honorably without fighting when surrounded.

3. Nationalism and the mass army:
This relatively bloodless period ended with the levée en masse—the “nation in arms”—in Revolutionary France, which drafted unmarried men aged eighteen to twenty-five. These delivered an almost inexhaustible supply of cannon fodder courtesy of the new ideology of nationalism, an unprecedented force multiplier. Napoleon’s Grande Armée, which took him to the gates of Moscow, numbered six hundred thousand, an unparalleled size.

In war, invention always breeds imitation, and so Europe and America copied conscription. The result was mayhem to the max. The dress rehearsal was the U.S. Civil War, with both sides raising three million men over four years. Flanked by the mighty idea of slave emancipation, technology yielded a new force multiplier. Every lethal device that would later kill millions in two world wars save tank and poison gas came onstage. These were the fast-loading repeating rifle, an early machine gun enabling one man to fell a dozen, barbed wire that bled an attacking force dry, rocket launchers, railroad and telegraph that quickly delivered masses to the front. Add grenades and mines, ironclads and subs. The Union Army even fielded an air force of sorts: reconnaissance balloons. Fifty years later, these new weapons felled eleven million fell in World War I, followed by nearly double that in World War II and fifty million civilian deaths. 

These wars set the pattern for the rest of the 20^th century, though on a more modest scale. At, best, hundreds of thousands, not millions, were going after each other—luckily outside of exhausted Europe. They were propelled by tanks, aircraft, combat ships, long-range rocketry, and precision munitions. The last classical battle—army vs. army—was fought in Iraq in 2003. 20^th-century warfare moved off-stage, though with one atypical exception in our day: the full-scale Russian assault on Ukraine in 2022, which has bogged down in a war of attrition reminiscent of the First World War.

War in the 21^st Century

Clausewitz remains on target with his key dictum: The central purpose of war is to break the enemy’s will. A carryover from the previous century are internal wars such as those in Afghanistan, Yemen, Sudan, the former Yugoslavia, and Libya. These are driven by factions, creeds, and ethnicities. Invariably, they draw in foreign players either indirectly or openly, as with NATO’s bombing campaigns against Serbia and Libya. Internal carnage and outside intervention are fixtures of our era. 

A second emblematic feature is war against non-state actors like Hezbollah, ISIS, and Hamas. A third constant is proxy wars going back to Korea, Vietnam, and Afghanistan in the Eighties, where the real targets of American might were Beijing and Moscow. Today, Iran backs up Hamas and Hezbollah. These three types of war have reached into our century, sticking out in a multihued pattern of collective violence.

On the level of theory, Clausewitz might be confused by the sheer number of unfamiliar contestants, and he would be flummoxed by the infinite variety of tactics and means. But he would understand how revolutionary technologies change the nature war, and he would marvel at the lopsided new force-exchange ratios not seen in the past. A cheap drone can kill a multimillion-dollar tank, a $500 missile can outfox Israel’s Iron Dome projectiles that cost about $50,000 a piece. That is a ratio of a hundred to one. Specks on the water, a swarm of low-cost Iranian speed boats in the Gulf could wreak havoc on a state-of-the art U.S. frigate that carries a price tag of $1.2 billion. 

Nor are the weak technological babes in the woods, as were American, Asian, and African natives in the 19^th century. The rapid diffusion of ultra-modern gear delivered by sponsoring powers like China and Russia blunts the traditional edge of the industrial players of yore whose Maxim guns and gun boats used to best bows and arrows. But beware of the dialectics of war, Clausewitz would interject: Technology begets counter-technology. Established states are not stupid, either. To stymie waves of unsophisticated missiles, Israel has fielded Iron Sting, a mobile laser-beam device energized by a few shekels’ worth of electricity. 

Clausewitz did not focus on urban warfare, the New Normal in the Middle East. Hordes of pundits predicted after “10/7” that Israel would be bogged down in Gaza’s tunnel labyrinth, suffering unacceptable casualties. After two months, the death toll was around 100. As always, adaptation rules. ­The Israel Defense Forces (IDF) have deployed new tactics and tools that trumped the familiar advantage of the locals. For instance, they have developed low-yield munitions that take out snipers on the eighth floor of a high-rise without leveling the rest. Quickly-jelling chemicals seal tunnels, saving the lives of Israeli soldiers who otherwise would have to go mano-a-mano in the maze. Robot vehicles sniff out traps and combatants. Armored bulldozers neutralize IEDs in the streets above. Blocking fuel deliveries into Gaza, Israel has hampered the enemy’s mobility. Cutting off internet and electricity rendered him deaf and blind. By contrast, the IDF was not exactly “eyeless in Gaza,” to recall the eponymous novel by Aldous Huxley.

So much for technology and tactics. The advantage today, though, tilts sharply in favor of non-state actors in the larger political setting. The costs for states are not only denominated in dollars. In the 19^th century, Clausewitz could not foresee how global politics would batter the justice of Israel’s cause as victim of Hamas’ murderous aggression. Predictably, the tables quickly turned.

With thousands of Gazans killed, according to the Hamas-run Health Ministry, the Jewish state became the greater evil, which placed massive Western pressure on Jerusalem. For Hamas (as for Hezbollah in Israel’s war with Lebanon of 2006), their own dead civilians are more valuable than Israeli terror victims in the “battle of images.” Indeed, hiding behind human shields is the name of the cynical game. If you are not Hafez al-Assad, who murdered three hundred thousand of his own in Syria, counterattacks come with a short “sell-by” date. Time is the worst enemy of urban warriors hailing from the democratic world. This handicap does not beset Vladimir Putin, who systematically levels Ukraine’s civilian infrastructure—schools, hospitals, dams—or Russia’s earlier war of annihilation in Chechnya.

Nor could the Master descry wars of regime change and democracy promotion, as fought by the United States in Afghanistan and Iraq. The targets of “re-education” won in the end because their stakes were far higher than the invader’s. Outsiders can always go home; the locals have no other place to go. In Kabul, the Taliban are back. Iraq, once a strategic bulwark against Iran, is a faltering state under the knout of Tehran, America’s worst foe in the Greater Middle East. Eighteenth-century rulers did not care about the coloration of the regime next door, nor about the legitimacy of their attacks. Frequent wars of succession were not about monarchy vs. democracy, just about the person on the throne. The lode star was cold-eyed realpolitik for the sake of security or aggrandizement. And there was no BBC or CNN putting devastation onscreen 24/7.

The largest lacuna in Clausewitz’s theory are the prox­y wars of the 20^th and 21^st centuries. Today, they dominate the battlefield for a simple reason: The great powers are terrorized by the specter of nuclear war. So, they move into regional conflicts as distant suppliers, not as combatants. China and Iran support Russia to weaken the United States, while the West pumps cash and hardware into Ukraine. Balancing is the name of the game. Tehran supplies Hezbollah and Hamas to blunt America’s “continental sword” in the Middle East, Israel. In the shadow of nukes, power is deployed at one step removed to dominate and deter—like U.S. battle groups in the Eastern Mediterranean and the Western Pacific in 2023. 

Next to proxy war, behold oblique war. The best example is China. Eager to expel the United States from the penthouse of global power, Beijing extends its non-military tentacles round the planet. It builds competing economic institutions. It buys up ports in Europe. It sabotages U.S. embargoes by importing Iranian oil in vast quantities, which keeps the regime afloat. China intimidates U.S. allies in the Far East— Taiwan, Japan, the Philippines, and Australia—with military threats. Xi Jinping labors as dishonest broker in the Moscow-Kyiv war and in the Middle East to amass political advantage. Why war if you can score without it? 

The overall strategy is indirect war, which did not preoccupy Clausewitz, who thought in terms of bullets and battalions. Start with Putin’s “Little Green Men,” who invaded Crimea in 2014 and might do so again in the Baltics. Bereft of insignia, such troops might not trigger NATO’s Article 5. Go from indirect to invisible war, nowhere to be seen in Clausewitz’s era: subversion, election-rigging, mind manipulation, fake news to spread defamation. War on the inside is a cheap substitute for the real thing.

Look back: In World War II, the Allies were reduced to deploying short-wave BBC broadcasts few Germans could receive; Der Fuhrer had made sure to leave the masses with one-station radios blaring out government propaganda. Dropping leaflets from high-flying bombers did not exactly reach the right target audience. With digital media like X and Telegram, Russia and China can reach into the brains of millions with a few strokes of the keys—no fingerprints. Disguise also favors more deadly stuff like cyberattacks on a country’s assets, be they military or civilian, no bombs needed. How to detect and deter no-name aggression? 

The Moral of this Tale

Clausewitz’s principles of war will never fade, but the practice keeps changing like a rotating kaleidoscope. In that respect, Putin’s war of conquest looks like a throwback to an earlier era. Contemporary warfare beyond Ukraine is not about marching army corps. The modern toolkit ranges from subversion to internal mayhem, from proxy wars to disarming strikes like those against ISIS and Hamas, from the chess game of political advantage to the no-name warfare of mind manipulation and cyberattacks. “Anything goes,” postmodernity proclaims—but we must hope that “no nukes” holds.

On the underlying dynamics, Clausewitz remains up to date. “War is . . . an act of force to compel our enemy to do our will”—whether by flintlock or laser beam. Running for 750 pages, On War, alas, is not an easy read. In the world’s military academies delving in is a must.

Josef Joffe, a member of the American Purpose editorial board, is a distinguished fellow at Stanford University and has taught international politics at Harvard, Stanford, and Johns Hopkins universities.

Image: Sailors aboard the USS Carney stand watch during an operation to defeat a combination of Houthi missiles and unmanned aerial vehicles in the Red Sea, Oct. 19, 2023. (U.S. Navy)