A man walks past destroyed buildings in a neighborhood of Aleppo, Syria, that was recently targeted by regime airstrikes. (Karam Al-Masri/AFP/Getty Images)

The recent bombing of a hospital in Aleppo portends a longer, bloodier siege of Syria’s largest city and vital commercial center. In what could be a turning point in the five-year war, the pending siege of Aleppo has an eerie yet informative parallel to a previous conflict: the siege of Sarajevo in Bosnia. The dynamics of that 1992 to 1995 battle hold important lessons for Syria, as diplomatic attempts at cease-fires falter and the world grapples with a menu of unsatisfactory military options.

The siege of Sarajevo was the longest siege of a major city in modern warfare. Like the Syrian regime, the Bosnian Serbs held a large military advantage over their Bosnian Muslim (Bosniak) and Bosnian Croat opponents in the Bosnian army. But despite their military advantage, the Bosnian Serbs did not capture the city outright. The victims of the siege described it as an act of cowardice — blockading the city and forcing a slow war of attrition risked fewer casualties. However, senior Bosnian military officials we spoke to during our field work last summer described the prolonged siege differently: By committing the fewest forces possible to keep the Bosnian army tied down and the international gaze fixed on the capital, they could free up forces elsewhere. Their goal, with the backing of Serbia, was never to seize the capital in one decisive battle.

For that approach to work, conditions in Sarajevo had to be bad enough to gain international attention, but not bad enough to compel the international community to intervene militarily. To strike that balance, Bosnian military leaders we spoke to suggested that the Bosnian Serbs purposefully left supply routes open. The most notable was an intricate tunnel system. This underground network became the Bosnian army’s main way of transporting food, humanitarian supplies and weapons into the city and prevented Sarajevo from deteriorating into chaos.

We see similar dynamics in Aleppo. The Syrian forces have until recently appeared to allow so-called “humanitarian corridors” to exist as supply routes to rebels, as well as more than 200,000 citizens holed up in Aleppo’s eastern neighborhoods. This may be an intentional way to keep Aleppo in a state of suspended animation but not devastated to the point of triggering a pro-rebel military intervention from NATO-backed forces. However, if Aleppo is a distraction like Sarajevo was, the question becomes: Where else should the international community be watching right now?

The siege of Sarajevo holds other important strategic lessons for understanding the Syrian context. First, in Sarajevo, neither side had an effective approach to fighting in a major urban area, falling into static positions reminiscent of World War I trench warfare from which neither could break the stalemate. We should expect the same in Aleppo: If the forces aligned with the Syrian regime want a quick and decisive military victory, they probably cannot achieve it, even with Russian air support.

Second, an important aspect of the defense of any city is how its citizens mobilize to protect their neighborhoods. In the case of Sarajevo, a small core of Bosnian army soldiers in the city itself relied heavily on ordinary citizens taking up arms to protect the city. These ad hoc groups of citizen-soldiers organized around existing social structures and in some cases around underground criminal networks. Aleppo is a sprawling city of merchants, or bazaaris, without an organizational core similar to the Bosnian army, and it’s unclear if rebel-held areas can leverage similar networks to mobilize citizens to withstand a long siege.

A third point is that the Bosnian Serbs previously had fought a costly battle trying to capture a city — Vukovar in Croatia — and had become more casualty-averse. Similarly, Syria’s military has fought a number of pitched urban battles — in Homs, Hama and Palmyra, among others — relying on a number of indiscriminate tactics, from chemical weapons to crude barrel bombs, with mixed results. But unlike in Sarajevo, the Syrian regime’s motivation for besieging Aleppo is not one of gun-shyness or aversion to casualties but rather a punitive yet calibrated attempt to avoid committing too many ground forces.

A final lesson of Sarajevo is that cease-fires can be effective in ending a siege but can also be counterproductive. A May 1992 cease-fire succeeded in exchanging the kidnapped Bosnian President Alija Izetbegović for a number of Yugoslavian National Army (JNA) forces who were surrounded in the city. However, the cease-fire also demonstrated that the JNA forces could not be a moderating force in the city, leading to greater emphasis on the building of the Bosnian army and what became the Bosnian Serb Army (VRS). Even when handled well, cease-fires can harden or radicalize the existing positions. Arguably, similar dynamics are present in Aleppo.

Another battle from the Bosnian war is instructional on this point: the battle of Mostar. In this, smaller Bosnian, Bosniak and Bosnian Croat forces defeated the Bosnian Serb forces relatively quickly in 1992. But when the Croats turned on the Bosniaks for control of Mostar, the conflict devolved into a violent, two-year stalemate in which neither force could defeat the other. Given Syria’s divided opposition, we can expect similar dynamics to emerge should the rebels retake a major urban center like Aleppo. The fractious nature of Syria’s opposition makes it difficult to imagine a scenario in which a battle for Aleppo does not devolve into a quagmire of localized fighting.

The siege of Sarajevo ended only after the international community intervened and eventually forced the Bosnian Serbs to negotiate the 1995 Dayton Accords. In Aleppo, the Russians have militarily intervened on the side of Assad’s forces, but not enough to permanently tip the local balance of power. If history teaches us anything, it’s that we cannot expect a lasting peace without an overwhelming third party intervention to force the belligerents to the table. The question is whether that third party will be Russia, NATO-backed forces or Russia and NATO-backed forces working together in some marriage of convenience.

Ostensibly, the point of any siege is to shatter the enemy’s morale and willingness to fight, not to go block by block to conquer the city. Initially a form of warfare popularized by the Romans, sieges were used to slow-bleed a city’s inhabitants into surrendering after an initial urban assault had proved ineffective. Whereas strong fortifications during medieval times favored the defense — as MIT’s Stephen van Evera has noted — siege warfare, enabled by greater infantry weapons from cheaper iron, favored the offense. But in modern times, greater urban sprawl that acts as a de facto buffer zone, denser urban terrain and greater connectivity have arguably made siege warfare more challenging for the offense. Even with the assistance of Russian arms and aircraft, the stronger Syrian military has been unable to dislodge modest Syrian rebel forces from their entrenched positions.

Of course, there are important differences between Bosnia and Syria. Aleppo is strategically a bigger prize for whomever controls it than Sarajevo was, given its location along an important crossroads. Moreover, the opposition fighters in Aleppo are more splintered and lack the command and control of their Bosniak counterparts. Further, Bosnia’s physical location in Europe made the potential for outside intervention more plausible, giving third parties more leverage. Finally, the physical devastation and human displacement, while severe in the Bosnia case, was not nearly on the same scale as Syria’s. Buildings and blocks in Sarajevo remain pockmarked to this day but are roughly intact. In contrast, much of Aleppo has been reduced to rubble.

Still, the modern history of siege warfare suggests a long war of attrition in Aleppo, a drawn-out battle rather than an all-out provocative attack to end the war in one fell swoop. Unlike siege warfare of the medieval age, the current layout of cities arguably may favor the defense, thus making attrition-style warfare more likely. As a result, the pending siege of Aleppo could last years and lead to tens of thousands of more Syrian lives lost or uprooted.

The hashtag #AleppoisBurning is an appropriate framing device for the battle for Aleppo, but expect a slow burn rather than a raging inferno. We have a road map on how sieges in modern warfare unfold. Sarajevo survived its siege, thanks to a successful intervention. Aleppo’s future is yet to be seen.

Maj. Mike Jackson and Lionel Beehner are, respectively, the deputy director and director of research of the Modern War Institute at the U.S. Military Academy at West Point. The views here are those of the authors and do not reflect the views of the Department of Defense, the U.S. Army, or West Point.