I want to respond to two ideas bouncing around both here and on reddit related to Russia’s actions in Russia as they relate to Ukraine. Specifically, the idea that a Ukrainian invasion of Russia would prompt some kind of escalation from Moscow, and therefore, Ukraine should not invade Russia for fear of ‘giving Russia an excuse’ to do something. The reality is that an invasion of Russia is already a foregone conclusion. The threat of the ‘Russian Reaction’ has very little to do with Ukraine’s actions.
Belgorod
During the current phase of the conflict, pursuit of the collapsing Russian forces could allow Ukraine to smash the border line and seize Belgorod or Kursk. They won’t for two reasons:
First, it wouldn’t help. Large sections of Ukraine are suffering under a genocidal occupation that is systematically murdering Ukrainians, destroying infrastructure and history, and worse. Every shell, and every gallon of gasoline used to invade Russia is one not used to liberate Ukrainian citizens. Leaving Ukrainian cities to Russian occupation is simply intolerable. Even if Ukraine attempted a counterweight strategy, there is no reason to believe that Russia would stop their reign of terror during peace negotiations.
Second, there is the potential reaction of the lukewarm European powers countries. An invasion of Russia would allow those countries, or pro-Russia factions within them, to advocate for a ‘negotiated settlement’, and to meddle in the support for sanctions or arms support for Ukraine. As long as Ukraine holds no territory outside their 1991 borders, that source of controversy is minimized.
Crimea
Crimea is Russia. I mean, it isn’t, and we all know that. But recall that Russia has formally annexed Crimea, and Sevastopol has been a major Russian naval base for some time before that, leased from Ukraine. From the Russian legal and propaganda perspective, both Belgorod and Voinika are ‘Russia Proper’.
Ukraine has sworn to reclaim everything back to the 1991 borders. That means invading Crimea if Russia does not cede it themselves, which Russia has shown no intention of doing. That means, from the Russian perspective at least, that Ukraine has sworn to invade Russia. That confrontation is already going to happen.
Moscow
There is a military force in Ukraine fighting the Russian invasion under a bi-color flag that has stated in no uncertain terms that they intend to take Moscow next. That force is the Freedom of Russia Legion. Those forces will be trained in Ukraine, equipped with formerly Russian weapons repaired and overhauled in Ukraine, and will attack from Ukrainian territory. The rest of the world may see this as an internal conflict, unless the Russian government is actively imploding, this will absolutely be viewed as a Ukrainian incursion.
Mobilization
A common response to the idea that Ukraine shouldn’t invade Russia or attack Russia is because it could ‘give the Russians an excuse to mobilize’. Ukraine has already conducted airstrikes and commando raids into Russia, and that wasn’t enough to trigger a mobilization of the Russian population. Let’s play what-id and ask what if Russia does mobilize in response to a Ukrainian incursion?
I will point out that the mobilization would not work to respond to any action Ukraine might take. Moscow has already been conducting a covert mobilization of their subjects, poor, and other groups (criminals, etc) already. They’ve already resorted to impressment in occupied territories, and active recruitment in their ‘core cities’. That means Russia has already exhausted all of their ‘easy’ recruits and would need to resort to conscription from an indifferent to hostile populace. Let’s ignore for a moment the questions about whether or not Russia could mobilize Moscow and not collapse. Instead, it is key to point out that the mobilization would take time.
First you need to assemble the conscripts, which in the case of unwilling conscripts means rounding them up. What is achievable? 1000 per day? 5000? Even at 5000 per day, it would still take three weeks to simply assemble a force of 100,000 to form a new Army to counter a major incursion and defend a reasonable front.
The second issue is training. Ukraine has managed to assemble real offensive combat power. It takes development of opposing combat power to stop it, which means that untrained troops won’t cut it. And it takes 6-8 weeks to go through the absolute minimum training to develop combat power. Then add in all of the logistics issues of equipment, food, uniforms, weapons, etc. The reality is that any attempt to ‘mobilize’ Russia in response to anything won’t bear any fruit for a minimum of 2 months.
Nuclear Weapons
Nope. The main problem is that nukes won’t work. Russia can’t manage the intel to target dynamic forces and military formations with their cruise and ballistic missiles. If the Russians can’t find Ukrainian forces to target them with cruise missiles, then using tactical nuclear weapons is going to make bigger holes in places that Ukrainian forces aren’t. To use nuclear weapons to blunt an actual advance would require the use of significant number of strategic weapons saturating an area. a 1MT warhead can destroy infantry in the open to 12km. In bunkers and vehicles out to a much smaller radius. To cover a 120km front would take at least 5 of the infernal things, 10 if you’re not sure where the advancing troops are and go 2 deep.
The response from the international community would likely be extreme, and there would be a real risk that NATO would go kinetic, conventionally or otherwise. There would be even odds that the US, UK, or France would initiate a nuclear first strike against Russia’s nuclear forces in response. Use of nuclear weapons on that scale is a suicide move. Not in the context of Russia generally, which it would be, but as a personal decision for the officers involved in the launch. If morale in the Russian military degrades any further, self preservation will cause officers to refuse to validate orders to launch, or perhaps even refuse orders to arm and deploy Russia’s nukes.
I do think there is a reasonable risk that Russia might attempt to use tactical nuclear weapons in the vicinity of Oryel or Bryansk in response to the Freedom of Russia legion bearing down in a drive to Moscow, but as it would be limited to Russian territory, it would be less of and international issue and more a domestic tragedy.
Conclusion
A Ukrainian invasion of Russia, at least as seen from the Russian perspective, is a near certainty. Any discussion of limits about whether Ukraine ‘should’ or ‘shouldn’t’ do something on Russian soil are basically moot. The main issue for Ukraine is that they still have limited combat power, and liberating Ukrainian territory is their priority.
Later in the war, perhaps next year, things could be very different. If Ukraine has liberated most of all of their territory, and Russia uses the winter to try to mobilize new combat forces, managing to find new sources of weapons and continuing their attacks, the front lines could well move within the Russian federation. If Russia doesn’t implode first.