Ukraine has huge, untapped gas reserves. If they start mining them - which they were about to before the Crimean invasion - then there's no reason for Germany and western Europe to keep doing business with Russia, effectively bankrupting the Russian state. I don't know what effect western companies leaving Russia now will have, given that the plants are already there - Russia will certainly still keep producing its own gas, with our without the west's help.

This is fundamentally another petro-war, all of the media/ideological stuff about de-nazification or the mighty Russian ethno-state is bullshit. It's money and oil.