As a wikipedia certified PhD in geopolitics and macroeconomics I have come to offer my professional opinion.
In all seriousness I did take some upper level macro classes in college, but actually I'm not sure that is necessarily the most relevant field to answer this question. I think you need to look at a couple of areas to answer this question as it is not purely economic. However, that's where I will start.
Russia has been insulating itself from potential sanctions for some time. This has been a very deliberate and intentional effort to be able to continue a conflict in exactly the situation they are in now.
Over the same period, Moscow has tried to wean its oil-dependent economy off the dollar, limited government spending and stockpiled foreign currencies.
Putin's economic planners have sought to boost domestic production of certain goods by blocking equivalent products from abroad. Moscow has meanwhile amassed a war chest of $630 billion in international reserves — a huge sum compared to most other countries.
David Lubin, a Citi economist and associate fellow at Chatham House, said "fortress economics" requires the creation of big foreign currency reserves that can be spent if sanctions bite.
Well aware of this, US sanctions have targeted some weak points in the 'fortress'.
The United States is also trying to hobble Russian military and industrial companies by preventing them from buying critical technology such as advanced computer chips.
Vladimir Putin has been expecting the West.
www.cnn.com
However, Putin has been strategically nationalizing the Russian economy. Of course recently he has threatened to nationalize companies that leave Russia, but he has been making sure there is state control over important sectors for some time.
government control is now highly concentrated in energy, banking and a handful of other, often “strategic” sectors—perhaps not surprising considering the topic of Putin’s
somewhat controversial dissertation on strategic planning and state control of resources.
(Source)
It's also worth noting that in addition to those sectors, the Russian rail company is also nationalized. This is important as rail is critical to Russian logistics.
Russian
army logistics forces are not designed for a large-scale ground offensive far from their railroads. Inside maneuver units, Russian sustainment units are a size lower than their Western counterparts....The reason Russia is unique in having railroad brigades is that logistically, Russian forces are tied to railroad from factory to army depot and to combined arms army and, where possible, to the division/brigade level. No other European nation uses railroads to the extent that the Russian army does. Part of the reason is that Russia is so vast — over 6,000 miles from one end to the other.
I highly recommend reading this article. It is rather long but very insightful.
Editor's note: Don't miss our comprehensive guide to Russia's war against Ukraine. Russia’s military buildup along the border with Ukraine has
warontherocks.com
Now, Russia also technically has access to all the resources it need internally to continue this conflict. Oil, food, and manpower. It has already nationalized many of its industries. You mentioned later that there aren't any examples of a market economy maintaining a conflict while economically isolated. Well, Putin is quickly moving Russia away from a market and towards full war mobilization.
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