Russian troops

Will Russia Invade Ukraine (Again)?

April 14, 2021
Simon Saradzhyan

This analysis is a slightly updated version of the original published by Defence-in-Depth, the research blog of the defense studies department at King’s College London.

Not a day goes by without dire warnings of an imminent Russian military invasion of Ukraine. Such warnings do not come out of the blue: A variety of sources—including government organizations, such as U.S. and Ukrainian intelligence, military and diplomatic agencies, and non-governmental organizations, such as Jane’s and Russia’s Conflict Intelligence Team—are reporting that the Russian military is amassing assets, including infantry, airborne, artillery, missile and tank units, in regions adjacent to Ukraine in numbers unseen since 2014.  While the concentration of Russian tactical battalion groups vis-à-vis Ukraine is hardly disputable, tentative results of my research into the Russian leadership’s past decisions regarding military interventions indicates that Russian President Vladimir Putin is unlikely to order these combat units to conduct an offensive against Ukraine unless Ukrainian President Volodymyr Zelensky makes the first military move on the Donbass chessboard. I have examined nine instances when Putin was likely to have considered ordering a military intervention in a foreign country but decided against it, and three instances when he did end up issuing such an order (Georgia in 2008, Ukraine in 2014 and Syria 2015). My examination of these 12 instances revealed that for Putin to issue such an order, a confluence of three conditions needs to be present. First, Putin has to see a clear, acute threat to one or more of Russia’s vital national interests as he sees them (Table 1). Second, he has to have a reasonable hope that a military intervention would succeed in defending the threatened vital interests or advancing them. Third, Putin has either to have run out of options that do not involve the massive use of armed forces, and therefore are generally less costly, or to lack the time needed to exercise such non-military options to respond to the perceived threats. I don’t believe that Putin, who is the ultimate decision-maker when it comes to Russia’s foreign and defense policies, sees either the first or third of these conditions when he looks at Ukraine.

First, when it comes to Ukraine, neither of the existing threats to Russia’s vital interests, such as preventing armed conflicts waged against its allies and preventing the arrival of hostile regional hegemonies on Russia’s borders, have become qualitatively more acute recently, nor have new threats emerged. The probability that NATO, which Russia’s leadership views as a threat to their country’s national security, will accept Ukraine as a member has not increased. Yes, Zelensky has made several appeals to the alliance recently, arguing that a path toward NATO membership is the only way to end war in eastern Ukraine. However, while NATO Secretary-General Jens Stoltenberg’s response to these appeals included expression of support for Ukraine’s territorial integrity, he kept mum on whether the alliance would offer Ukraine a membership action plan (MAP). NATO did promise Ukraine in 2008 that it would join the alliance one day, but that day has not recently become any closer. In addition to the expansion of NATO to include Ukraine, Putin’s aides have also made it clear that a Ukrainian offensive in Donbass, where several hundreds of thousands have acquired Russian citizenship, would be treated as crossing a Russian red line. “I support the assessments that also exist inside Ukraine that the beginning of hostilities [in eastern Ukraine] is the beginning of the end of Ukraine,” Putin’s deputy chief of staff Dmitry Kozak said. “It’s a self-inflicted wound, a shot not in the leg but in the face,” he said, adding that Moscow “would have to come to the defense” of Russian citizens in eastern Ukraine “depending on the scale of the fire.” These explicit warnings may have been, perhaps, one reason why chief of the general staff of the Ukrainian Armed Forces Ruslan Khomchak publicly pledged that his forces, which have been concentrating in areas adjacent to Donbass, would not launch an all-out offensive against the pro-Russian separatists in Donbass. (Were, however, Ukraine’s leadership to break its promise and order such an offensive against Donbass, where more than half a million people hold Russian citizenship, or were NATO to offer Ukraine a MAP, the first of the conditions necessary for Russian military intervention would emerge, altering Putin’s calculus; it seems unlikely, at the time of this writing, that either would occur in the near future.)

Second, as long as Ukraine doesn’t make the first military move in Donbass, I doubt that a Russian offensive against this country would advance any Russian vital interests, such as preventing armed conflicts waged against its allies, or advance such interests, such as preventing the arrival of hostile regional hegemonies on Russia’s borders. Such an offensive will not put a decisive end to Ukraine’s NATO aspirations unless Russian tanks manage to roll all the way to Ukraine’s western frontiers. Moreover, even a limited Russian intervention can yield significant net costs for Russia. Yes, Russia’s armed forces do operate more tanks, artillery, multiple rocket launch systems, missiles, warplanes and other systems than their Ukrainian counterparts, and these systems are generally more advanced than those in the Ukrainian arsenal. In addition, Russia has far more professional soldiers in its armed forces than Ukraine does. However, it is not clear whether all these qualitative and quantitative advantages would be sufficient to offset the fact that the Russian Army’s numeric superiority over the Ukrainian Army would fall short of the minimum 3:1 ratio the attacking side needs to prevail, ceteris paribus. That ratio would still be much closer to 2:1 than to 3:1 even if the entire Russian ground force were somehow employed in the offensive, along with the Donbass’ separatist forces, estimated at 50,000. When calculating the correlation of forces, one should also factor in that the Ukrainian armed forces have acquired some advanced systems, such as U.S. Javelin anti-tank missiles and counter-battery radar, that would definitely make life, or, rather, combat, more difficult for the attacking ground force. That the Ukrainian war machine now has a functioning chain of command and that the Ukrainian military has spent the past several years preparing to repel an offensive from the east also indicate that a hypothetical Spring 2021 campaign won’t be a walk in the park of the kind that Russia’s “little green men” enjoyed in Crimea in Spring 2014. Even if Russia were to limit the offensive to marching more than 300 kilometers to establish a land bridge to water-starved Crimea, its offensive force could still suffer significant casualties that the Kremlin would find difficult to conceal or justify (unless that offensive came as a counter-offensive in response to a major Ukrainian attack). This failure, in turn, could result in a significant decline of the Russian leadership’s approval rating in contrast to the surge in public support that Putin enjoyed after an almost bloodless taking of Crimea. Putin can always count on his rating to eventually rebound by the next presidential elections in March 2024, but his United Russia party, whose popularity has been declining, may find it difficult to retain the commanding heights in the State Duma when parliamentary elections roll around in September 2021. And the further west Russian forces would advance, the more likely it would be that this military campaign would have to be followed by a lengthy counter-insurgency operation in lands where sympathizers of Russia are scarce compared to the traditionally pro-Russian parts of eastern and south-eastern Ukraine. More important, unless Russian tanks roll all the way to the western borders of Ukraine, the Ukrainian government would still probably refuse to abandon its efforts to win NATO membership and reorient toward Moscow, therefore denying Russia the benefit of advancing its vital interests (Table 1). The financial and economic costs of an all-out war initiated by Russia against Ukraine would also be significant, including Western sanctions “from hell,” such as a ban on all high-tech exports to Russia and its exclusion from SWIFT. And then, of course, there would also be the burden of subsidizing newly acquired territories, which can be quite significant, as the case of Crimea has shown. Even in their totality, these costs may still prove to be manageable for Putin as they would not cost him his post or threaten Russian statehood. Still, for a decision-maker as rational as Putin to agree to incur these costs, he has to see benefits that would outweigh them, such as the successful parrying of an acute threat either to a vital Russian national interest or to his own grip on power. As explained above, no such threat emanates from Ukraine at the moment.

Third and last, Putin has yet to run out of non-violent and therefore generally less costly options of defending and/or advancing Russia’s interests in Ukraine. That the Russian leadership believes it has not yet run out of such non-forceful options follows from the continued willingness on these leaders’ parts to engage in negotiations and other communications with Western political leaders and top commanders, whom Moscow expects to bring Ukraine to its senses. The demonstrative, unconcealed massive movements of Russian military units along their country’s border with Ukraine are also meant to signal Russia’s resolve to Kyiv and its Western partners, to compel Zelensky to stop what the Kremlin sees as deliberate efforts to stall negotiations on the implementation of the Minsk-2 agreements and to increase pressure on Russia via the newly-established Crimean Platform, which would bring together Western allies. The Russian movements are also meant to deter the Ukrainian leadership—who have apparently also ordered the movement of their troops in areas adjacent to the separatist-controlled parts of Donbass—to refrain from using these forces for an actual attack on the separatists.

Strong language—such as Kozak’s warning that a Ukrainian attack on Donbass will usher in the “beginning of the end of Ukraine” and Russian Foreign Ministry spokeswoman Maria Zakharova’s assertion that Ukraine’s NATO bid could “entail irreversible consequences for … Ukrainian statehood”—also demonstrates that the Kremlin so far hopes Ukraine can be deterred by words rather than by force.

So, if conditions for Putin to order a new major military intervention in Ukraine are not ripe, then why have Russian forces been amassing in areas adjacent to Ukraine? For one thing, the Russian military-political leadership may have concluded that the Ukrainian leadership has decided to try to change facts on the ground in Donbass by force and, therefore, the Russian military needs to be ready to intervene on the separatists’ behalf to beat back the Ukrainian offensive. In addition to signaling Putin’s resolve to prevent Ukraine from forcefully retaking Donbass, this concentration may also be meant to put pressure on Zelensky to stop what the Kremlin sees as the Ukrainian leadership’s efforts to duck out of implementing Minsk-2. This peace agreement, if implemented as agreed upon in 2015, would allow Kyiv to eventually re-establish control over Donbass, but on Moscow’s conditions, which would make Ukraine’s further drift toward NATO difficult. However, the Kremlin’s intention to employ its military for signaling rather than for actual fighting doesn’t preclude scenarios in which an accident could drag Russia and Ukraine into a war. Accidental wars have erupted more than once in the history of humankind, and for Russia and Ukraine to reduce the probability of an unintended war, they both need to reverse their military build-ups vis-à-vis each other.

Table 1: Russia’s vital national interests as seen by the Russian leadership 1

  1. Prevent, deter and reduce threats of: secession from Russia; insurgency within Russia or in areas adjacent to Russia; and armed conflicts waged against Russia, its allies or in the vicinity of Russian frontiers;
  1. Prevent emergence of hostile powers or regional hegemonies or failed states on Russian borders; ensure Russia is surrounded by friendly states, among which Russia can play a lead role and in cooperation with which it can thrive; 
  1. Establish and maintain productive relations, upon which Russian national interests hinge to a significant extent, with core European Union members, the United States and China; 
  1. Ensure the viability and stability of major markets for major flows of Russian exports and imports; 
  1. Ensure steady development and diversification of the Russian economy and its integration into global markets;
  1. Prevent neighbouring nations from acquiring nuclear arms and long-range delivery systems on Russian borders; secure nuclear weapons and materials;
  1. Prevent large-scale and/or sustained terrorist attacks on Russia;
  1. Ensure Russian allies’ survival and their active cooperation with Russia.

Table 2: Correlation of Russia’s and Ukraine’s military potential2




Ukraine's as % of Russia's

Ratio (rounded to whole numbers)

Military budget in national currency

3,087 bn roubles

117.8 bn hryvnia



Military budget in USD

$40.7 bn

$4.3 bn


81 : 9

Active military personnel, including




9 : 2





57 : 29





150 : 11

Aerospace Forces/Air Force




11 : 3





45 : 8

Reserve personnel




20 : 9


  1. I have chosen to synthesize descriptions of Putin’s Russia’s vital interests, which I define as conditions that are strictly necessary for the survival of Russia as a viable and successful state, from Russian leaders’ statements and strategic documents instead of simply quoting them. I did so for multiple reasons. One reason was the (perhaps deliberate) vagueness of the language that the authors of Russia’s recent strategic documents, such as the Military Doctrine of 2014 and the National Security Concept of 2015, have used to define and describe Russian national interests. More important, the 2015 document does not explicitly refer to some of the interests Russian leaders have identified in their statements, such as: the designation of the post-Soviet neighborhood as a zone of Russia’s privileged interests, including the national interest in preventing the emergence of hostile powers or regional hegemons in this neighborhood; the interest in ensuring that Russia is surrounded by friendly states, among which Russia can play a lead role and in cooperation with which it can thrive; and the interest in the survival of Russian allies. 
  2. Data from IISS' Military Balance 2021.

Simon Saradzhyan

Simon Saradzhyan is the founding director of Russia Matters.

Photo by the Russian Defense Ministry shared under a Creative Commons license. The opinions expressed herein are solely those of the author.

NB:  This is an evolving draft, as the author continues to refine his methodology.