As Russian reverses in Ukraine continue to mount Vladimir Putin has hastened to put down markers signaling that his country is willing to resort to desperate measures rather than fold and agree to at least a return to the pre-invasion status quo ante that would still leave Crimea and parts of Luhansk and Donetsk under Russian control. The partial mobilization, the "referenda" staged in areas occupied by Russia, and the extension of Russian military doctrine to these areas, are all intended to signal Russian resolve.
Foreign policy expert Gevorg Mirzayan claimed that Russia was taking off the gloves to dispel the illusion that Russia would capitulate:
"First, I’m talking about the illusion that Russia isn’t ready to go all the way. The special military operation status [as opposed to war], Moscow’s negligence in its military build-up measures, its demonstrative willingness to negotiate, its refusal to strike decision-making centers in Kyiv in response to the shelling of Russian territory by the Ukrainians - all gave an impression that a return to the status quo, which existed before the special military operation, could’ve been negotiated with Russia by recognizing Crimea and, possibly, Donbass [as part of Russia]...
"Thus, Moscow’s caution during the initial months of the SVO was perceived as a weakness, allowing Western politicians to employ negotiating methods with Russia (characteristic of the 1990s) that they were comfortable with: pressure, ultimatums, etc."
Now, said Mirzayan, Putin had set a clear boundary to Western escalation by warning the West that they risked a nuclear conflagration, if their precision weapons struck the annexed territories that had become an inseparable part of sovereign Russia:
"During all these months, the US and the EU have been walking on the edge regarding the issue of arms supplies to Ukraine: they were gradually increasing the volume and variety of arms supplied. They waited in order to see after crossing of what notorious red lines Russia’s harsh reaction would follow. The West went all the way from supplying equipment and non-lethal arms systems to providing 155mm howitzers (from which the DPR’s and LPR’s towns are being regularly shelled), as well as kamikaze UAVs, to the Kyiv regime.
"And now Vladimir Putin has made it clear that Russia will use all available arms, including nuclear arms, in order to defend national sovereignty and territorial integrity.
"The president didn’t elaborate further, but it would seem obvious to many that shelling the Russian city of Kherson or Donetsk with “HIMARS” or “CAESAR” howitzers supplied to the Kyiv regime during the conflict by the US and French governments could be perceived as just such an attempt [to threaten Russia's national sovereignty and territorial integrity].
To further emphasize the risks of a nuclear confrontation between Russia and the US, Russia's Ambassador to Washington Anatoly Antonov took to the pages of The National Interest with an article ominously titled "Cuban Missile Crisis 2.0 Over Ukraine?"
Antonov invoked that crisis at the start of his article:
"I have commenced my work on this article for two reasons. Firstly, this October will mark sixty years since the Cuban Missile Crisis when the USSR and the United States were on the verge of a nuclear conflict. This is an occasion to look closer at the foreign policy lessons that the two great powers have learned from that dramatic time. I believe that any American will see eye-to-eye with me that we must not allow the explosive situation of the 1960s to repeat. It is important that not only Russia and the United States, but also other nuclear states, confirmed in a common statement that a nuclear war cannot be won and must never be fought."
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Despite the confidence voiced in the opening paragraph that all sides agreed that a nuclear war and an explosive situation that could trigger it were impermissible, Antonov shifted to accusing the United States of creating such an explosive situation:
"Today it is obvious that the United States is directly involved in the military actions of the Kiev regime. Washington is openly building up the supply of lethal weapons to Ukraine and provides it with intelligence. They jointly plan military operations against the Russian Armed Forces. Ukrainians are being trained to use NATO military hardware in a fight."
"It feels like Russia is being tested to see how long it will remain patient and refrain from responding to blatantly adversarial actions and attacks. In fact, Washington is pushing the situation towards a direct confrontation of the major nuclear powers fraught with unpredictable consequences."
Anatoly Antonov (Source: Rbc.ru)
Andrei Sushentsev, dean of the Moscow State Institute of International Relations, and an expert on American foreign policy, who has taught at Georgetown and Johns Hopkins also harped on the comparison between today's Ukraine and Cuba in the 1960s. In an article titled "Is Ukraine an Eastern European Cuba?", Sushentsev effectively answered: It is much worse! Cuba could never threaten the US militarily, while Ukraine, an heir to Soviet military capabilities and constructing an army that matched Russia's army numerically, and with Western aid qualitatively. Those in power in Kiev viewed Russia as an existential threat because of its power of attraction for those identifying with Russia in east Ukraine, and therefore Ukraine was hell bent on defeating Russia and solving its identity problem in the process. The takeaway from the article is that if the US was willing to risk nuclear war over Cuba, it cannot expect Russia to do otherwise over Ukraine.
Sushentsev's article follows below: 
Andrey Sushentsev (Source: Foma.ru)
"In the course of the past three decades, the logic of Russia's relations with the Western countries has been built on the basic assumption that Moscow would accept any move by NATO to alter the balance of power in Europe. Indeed, Russia has often had to yield, which has gradually worsened its strategic position not only on the continent, but even in the belt on its immediate borders.
"This was the case until the West bet on Ukraine joining the transatlantic community, whose governments for years have built their national project on opposing Russia.
"Some experts compare Moscow – Kyiv relations with that of the US – Cuban relationship. Cuba, on the one hand, strived to be in the front line of the fight against global capitalism, while, on the other hand, was closely enmeshed in American socio-political life. The country facilitated the deployment of Soviet nuclear arms to confront the US, while lacking its own military potential to fight Washington. Nevertheless, there are factors that make the Russo-Ukrainian dissimilar to the conflicted relations between Washington and Havana.
"First, as opposed to Cuba, Ukraine began an intensive militarization and transformed itself into a significant military player in Eastern Europe. The powerful Soviet military capabilities (Kyiv was one of the major heirs of Soviet military potential after the collapse of the Union) were supplemented by NATO ones, which turned the Ukrainian Armed Forces into a new caliber of an army. According to various sources, Ukrainian army strength reached as many as 250,000 men, which is only a quarter of the Russian Armed Forces' numbers. If one combined them with reservists and employees of various Ukrainian security agencies, the number could total one million, which is comparable to the size of the Russian army. Today, all this power is engaged at the front.
"Second, Ukraine has an unresolved sociocultural conflict between people with a pro-Russian identity and those whose world outlook aligns with the Western Ukrainian national idea.
"The latter's tenure in power has predetermined a civil armed conflict with the country’s east. For 8 years, starting from 2014, the Donbass oblast has been under constant military pressure from Kyiv. Such a conflict ordained both the radicalization of people with Russian identity residing in Donbass and people of pro-Western orientation, who started to perceive Russia as an existential threat. The latter began to perceive their own assigned destiny in the defeat of Russia, believing that this would prompt the settlement of the civil conflict in the country’s east.
"Such a set of contradictions could be compared to the India - Pakistan dilemma, which are feuding for more than half a century over ownership of Jammu and Kashmir. Both countries emerged simultaneously upon the collapse of British India. For Pakistan, the ‘birth’ of its statehood is directly linked to the standoff against India. Both countries simultaneously build up substantial armed forces, including nuclear ones. Pakistan started to develop foreign policy relations with states hostile to India, trying to balance the threat emanating from New Delhi.
"Moscow perceived Ukraine as a similarly antagonistic country, realizing that in a few years it could get a significant quantity of arms from NATO member-states, which would suffice to inflict disproportionally large damage upon either Donbass or Russia itself. Moscow was faced with a dual strategic challenge. Given the background of Russia’s diminishing time-frame for negotiations, while Ukraine acquired the power potential sufficient to resolve the issue in the East, anti-Russian sentiments were rapidly growing in Ukraine itself.
"The combination of these factors explains why Russia calmly reacted to the two Scandinavian states' decision to join NATO. If one to compare the military capabilities of Finland and Sweden, it’s obvious that they are significantly inferior to those of Ukraine. Furthermore, socio-cultural contradictions between Russia and the Scandinavian countries are absent (as opposed to Ukraine’s case) where they are capable of leading to an instantaneous exacerbation of military conflict.
"Although this conflict remains an armed confrontation between two states, it will impact the entire world order architecture and alter the contours of Russia’s foreign policy strategy. The following are just some of the unknown elements of the new global equation: It is as yet unclear what will happen to the United Nations and what will be Russia's place in it? How will the world’s economy and logistics function? How and where will Russian energy resources be exported? Will the EU remain as economically stable and durable body, as it was with cheap Russian resources?
"Clearly, Russia’s relations with the West are changing qualitatively. The most comprehensible constant in these transformations is that Russia and NATO member-states will be adversaries (in the same way they were adversaries during the second half of the 1940s, a time of emerging rigid bipolarity. However, the contours of the shift in the US-European relationship can also be recorded.
"Now the Europeans will have no choice of partner. They’ll have to orient themselves solely to the US. Due to an incapacity for strategic diversification they’ll be forced to submit to NATO discipline. Since they have no option to cooperate with Russia, they’ll have to rely on American military protection, which will cost them much more dearly. In this respect, Europe would lose its strategic autonomy, which could probably be one of the main consequences of the unfolding crisis."