TL;DR: Ukraine will eventually either get nuclear protection by NATO or its own nukes, which in both cases will likely lead to the nuclear war with Russia. Knowing this, Putin may want to attack first or credibly threaten to do so.
The whole world is looking at the Ukraine-Russia conflict. Will it lead to nuclear war?
My general view is that the Ukraine-Russia conflict is structurally similar to the conflict between India and Pakistan. There are many differences, but it is a good reference point. Pakistan appeared after the British empire breakdown and it was a relatively new country whose borders was not well established. Kashmir is like Crimea in this conflict.
The bottom line of this analogy is that there will be many wars between Ukraine and Russia and that Ukraine will eventually become a nuclear power, the same way as Pakistan did, or will get similar military capabilities via drones and membership in NATO.
Putin also knows this and also knows that his large tank armies are almost obsolete. Therefore, he tries to limit future Ukraine military capabilities by attacking (or threatening) now. He does actually say this: we see Ukraine (in NATO) as an existential threat. He may also have some other irrational motives but the rational motives go beyond Putin, so any other Russian leader will be in the same strategic situation.
A nuclear war between Russia and Ukraine is rather possible from a long-term perspective, no matter how the current escalation will end. Unless the current war ends with the complete occupation of Ukraine.
Therefore, the real goal of the war may be taking (or permanently damaging) almost all Ukraine including all nuclear power stations and industrial capabilities. Personally, I do not think it will make Russia safer, as new military technologies (drones) will continue to evolve in other countries and Russia will be cut from new tech by enormous sanctions. In my view, the large war with Ukraine will end in large crimes and will be eventually lost because of international help.
Therefore, Putin may see the current moment as the only chance to stop future nuclear-protected Ukraine and to prevent a nuclear war with it.
Ukraine now is slowly developing medium-range missiles which can reach Moscow according to some accounts. ( Hrim-2 declared distance is 500 km, Poroshenko said 1000 km is possible.)
A rocket attack from Ukraine against Moscow, even if with a conventional warhead, will trigger Russian nuclear-powered anti-ballistic missiles. The nuclear explosions of such anti-missiles will be small (15kt?) and high-altitude, so there will be no harm, but it will be the first use of nuclear weapons in conflict for decades. A hypothetical future nuclear war of Russia with Ukraine could spill to other countries, as an attack by Ukraine on Russia could be seen as a hidden US attack.
Ukraine has a very large civil nuclear power – several stations of the size of Chernobyl (15 reactors). They could be used to produce plutonium. Ukraine has uranium ore mines. In 2019, the construction of nuclear fuel production plant was started (centrifuges?)
Ukraine non-nuclear status is based on the Budapest memorandum. 19 Feb in Munich Ukrainian president Zelensky almost threatened Ukraine’s rejection of the Budapest Memorandum: “I am initiating consultations in the framework of the Budapest Memorandum. The Minister of Foreign Affairs was commissioned to convene them. If they do not happen again or their results do not guarantee security for our country, Ukraine will have every right to believe that the Budapest Memorandum is not working and all the package decisions of 1994 are in doubt.”
The memorandum was signed on December 5, 1994, by the United Kingdom, Russia, the USA and Ukraine and provided guarantees of the security and territorial integrity of Ukraine in exchange for the renunciation of nuclear weapons. After the annexation of Crimea, the memorandum was clearly violated and Ukraine has “technical” right to demand its nuclear status back, or exchange this right for membership in NATO.
While NATO is a defence organization, Ukraine hopes that the membership in NATO will help Ukraine to attack Donbas and Crimea, which are its territories according to international laws – without risks of Russian retaliation. This situation will quickly deteriorate to war between NATO and Russia. Actually, nobody wants neither nuclear Ukraine, nor Ukraine in NATO, so NATO continues to feed Ukraine with promises without exact substance.
Ukraine unlikely will openly start to work on nukes soon, but it can ask for equal weapons in exchange for not doing so.
Therefore, for Putin, it is like a trolley problem: bad war now or hypothetical very bad war in the future. Personally, I am against changing the track in the trolley problem, as it is killing the real people for the possible safety of hypothetical people. Possible people and risks are more likely to be products of imagination and therefore many trolley-like problems are subject to biases – or just good words to cover some bad intentions.
In December 2021 Putin put a rather broad ultimatum to NATO: either provide safety guarantees to Russia or deal with military-technical consequences.
The wars are known to be unpredictable, so there is a risk that the current confrontation will spiral out of control into a global nuclear war. I even thought about moving to a county house from Moscow but decided to stay for now.
In some sense, it is a game of chicken on the trolley track.