For Russia what has happened in Ukraine since 2014 (and even since the Orange Revolution) has resulted in an existential threat. Putin and Lavrov have tried every which way to resolve this diplomatically but no dice. Ukraine, emphatically, is NOT an existential issue for the US, the UK or Europe. Obama said pretty much this several years ago. It is the leaders of these countries, without skin in the game, who seek refuge in war from the largely insolvable problems piling up at home.