The Russian invasion of Ukraine has proven to be a turning point in European security. As Ukrainians mount a stiff defense against a more heavily armed Russian invasion force, analysts and observers have raised the prospect of an ongoing resistance, one led not only by Ukrainian army units but also by civilian defense forces and ordinary citizens. This would amount to the first case of insurgent warfare within Europe in recent memory.

Anticipating the outcome of such a conflict is difficult. But if the history of modern insurgent warfare around the world is any guide, then the conflict is likely to be exceedingly violent and protracted, with difficult political implications. An insurgency may be unavoidable. But even if it does lead to a Russian defeat, Ukrainians—and the Western policymakers who are backing them—should not deceive themselves about just how awful insurgent warfare will be.

An Insurgency Will Be Violent

Insurgent warfare is asymmetric. Although there are widespread reports of supply chain interruptions and underprovisioned troops, the Russians have superior armaments than do the Ukrainians, and a larger army as well (although it is unclear how many Russian and Ukrainian soldiers are actively engaged in the present combat). This is what leads most analysts to conclude that the Ukrainians are unlikely to defeat the Russians on the battlefield. Insurgent warfare adapts to this asymmetric distribution of armaments and personnel by making any occupation acutely painful to the occupying force.

Specifically, an insurgency will be most successful if Russian soldiers are constantly frightened. To date, the Ukrainian resistance has shown great forbearance in its treatment of captured Russian soldiers, even reportedly allowing them to call their parents. If the war shifts to a hard-fought insurgency, their tactics are likely to become more brutal and violent.

Such a turn in the character of the violence would not occur because Ukrainians are by nature brutal, nor because their leadership seeks to inflict maximum casualties on their enemy as a war aim. Rather, this turn to violence would reflect the core logic of insurgency, which is to defeat enemy forces by making their occupation intolerable. The Ukrainian resistance will be most effective if Russians are on edge, sleepless, and prone to overreactions. Russian fear and disorganization will not only make the Russian occupying force vulnerable, but also harden the resolve of the Ukrainian resistance.

An Insurgency Will Be Long and Protracted

Insurgent warfare is designed to grind down the occupying force’s resolve. This does not happen in weeks or months, especially when Russian soldiers have the option of rotating back to Russia for some respite. Successful insurgent actions often take years to bear fruit.

In the meantime, the Russians may “control” Kyiv and other major cities during the day. They may install a puppet government, like the Soviet occupying force did in Afghanistan. And they may even declare an end to military operations to create the illusion of order, and hence to portray the insurgency as a threat to the postconflict peace. But asymmetric warfare and the Ukrainians’ total defense posture—which mobilizes not only active troops but also the whole of society to defend Ukrainian territory—together mean that the Ukrainian forces will seek to engage the enemy on their own terms, not the Russians’. This is how occupying forces come to pretend that they control an entire territory, when they actually only control the main roads in the main cities during daylight hours, a central problem facing US occupying forces in both Afghanistan and Vietnam.

The Politics of Insurgency Will Be Complicated

This may be the hardest truth for Western audiences who wish to see the Ukrainian resistance defeat the Russian occupying force. It is one thing to see former Ukrainian President Petro Poroshenko take up arms alongside his local self-defense force, or to see retired heavyweight boxer and Kyiv mayor Vitali Klitschko don combat gear. It is quite another to realize that Ukrainian civil society—like civil societies the world over—contains both liberal and illiberal elements.

This means that just as the Ukrainian government is encouraging citizens to take up arms in self-defense and distributing weapons to the population, it is providing arms to illiberal elements and criminal syndicates within Ukrainian society, including the Azov Battalion, a group that has attracted far-right elements, some of whom are self-professed neo-Nazis, but that forms part of Ukraine’s civil defense. Russia’s information campaign has already begun portraying the government in Kyiv as criminal and spoken of a campaign of “denazification” of Ukrainian society; it will seize on the presence of illiberal elements within Ukrainian society to further justify its occupation. Meanwhile, of course, the Russians will probably be courting the same groups that they are vilifying, trying to enlist them as Russian allies.

This means that supporting an insurgency means supporting—indirectly—illiberal elements and antidemocratic forces in Ukrainian society for the purpose of defending Ukrainian independence. This tragic choice is inevitable. And it will have far-reaching implications for Ukrainian politics and society even if Ukrainian forces are successful in expelling the Russian occupying force from their territory.

Looking Ahead

If the ongoing invasion of Ukraine ends up becoming a Russian occupation, Ukraine’s supporters will find themselves supporting what is likely to be a long, violent, politically messy insurgency. It is essential for anyone supporting the Ukrainian insurgency to confront this uncomfortable reality now. But does knowing this likely future offer any hope for avoiding it?

Ideally, supporters of the Ukrainian resistance would find mechanisms to channel money and weapons only to like-minded groups who reject extremism and crime. But a clear-eyed planner should realize that in irregular wars, Ukrainian forces will seek broad cooperation with any element that shares their strategic goals. As is often the case during war, common enemies make for allies of convenience. And war planners must also remember that the Russian occupiers may seek support from such extremist elements as well. There are no easy solutions to this difficult political calculation.

The most straightforward way to avoid a terrible insurgency in Ukraine is to avoid the occupation in the first place. In principle, Ukraine’s leaders could accomplish this by capitulating to Russian President Vladimir Putin’s demands now and surrendering Ukraine to Russia. But even if President Volodymyr Zelenskyy were to give in to Russia’s demands, allowing Putin to pick a pliable client government and demobilizing all armed elements within Ukraine, just one week of warfare seems to have hardened Ukrainian civil society against the Russian invading force. There may no longer be a negotiated solution to this war, even if Zelenskyy wishes to find one.

The other way to avoid such an insurgency is for someone—either the Ukrainians themselves, or an international coalition—to force the Russians out of Ukraine. At the moment, this seems unlikely, although the combination of robust economic sanctions and stiff resistance is making an ongoing occupation very costly. If Ukrainian forces and their international backers fail to prevent this occupation, they should steel themselves for a long and difficult insurgency in the months and years ahead.

Thomas B. Pepinsky is the Walter F. LaFeber professor of government and public policy at Cornell University and a nonresident senior fellow at the Brookings Institution.

The views expressed are those of the author and do not reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.

Image credit: Sgt. Alexander Rector, US Army