This article by emeritus Professor Paul Rogers gives some detail if of interest. Quoting some paragraphs below. As always, know situation v complex and academics in this area share different views on the v worrying situation..
www.opendemocracy.net/en/odr/russia-ukraine-crisis-whats-next-paul-rogers/
“When it comes to Russia, the safest assumption must be that the crisis stems from President Putin’s determination to put the country back in the superpower bracket, but this does not mean that Putin wants a full-scale war over Ukraine. To people of Putin’s generation, the way Russia was treated with near contempt after the collapse of the Soviet system 30 years ago still rankles, and it is surprising how few Western commentators factor this in.”
“Adding to the resentment is NATO’s slow encroachment into countries that much of Russia’s political elite still considers its ‘near abroad’ – with Ukraine being the main focus but also Poland and Romania. For example, one of the key elements currently sparking discontent is the US decision to establish anti-ballistic missile batteries at Redzikowo in Poland and Deveselu in Romania, using the Aegis Ashore system. Currently under construction, this combines advanced radar systems with interceptor rockets and has the stated purpose of protecting the West from ballistic missiles launched by ‘rogue states’ such as Iran. Moscow fears, though, that the Aegis system’s MK 41 launcher can readily be used for the Tomahawk cruise missile, the successor to the missiles of Greenham Common fame, for attacks on Russia itself.”
This raises questions over how far Putin intends to take the current crisis and whether there is actually a risk of a major war in Europe. One of the problems with Biden’s emphasis on releasing US intelligence about Russia’s military build-up is that it is relatively raw data, with the White House offering little interpretation from its own intelligence analysts. A relevant perspective on this is offered by the usually well-informed Jane’s Defence Weekly magazine. This reported on Tuesday, the day before the US predicted war, that:
“There appears to be little indication that Russian armed forces are mobilising en masse for a major war against Ukraine. A limited operation to support pro-Russian forces in the Donetsk and Luhansk regions appears more likely. [...]
“A significant Russian incursion against Ukraine would risk escalating into a major conventional conflict in which Russian troops would require substantial logistic support consisting of huge quantities of ammunition and fuel, as well as the activation of medical support facilities to deal with largescale casualties.”
Article goes on to say incursions in East Ukraine more likely but adds
“ In a sense, the two belligerents, Russia and NATO, are now locked into a thoroughly unstable embrace, always with the risk of unplanned escalations. It is a classic case of that annoying acronym AIM – accidents, incidents or mavericks – that can turn a crisis into something much worse. Mavericks in this case could be renegade pro-Russian militias in Donbas but could just as easily be some of Ukraine’s far-Right militias.”