Russia would not conduct a unilateral symetrical military invasion of Europe.
Why did Lenin cede so much Russian territory to the Central Powers in the Treaty of Brest-Litovsk? To buy time to consolidate power in Russia, so the Soviet Union could re-take those territories at a later date. Lenin sacrificed territory to guarantee the survival of his regime.
Putin will attempt the same. Putin's priority is the survival of his regime, the consolidation of his power, the elimination of his domestic rivals, and the re-building of the Russian military. If Putin can get former Soviet Republics, like Kazakhstan, to be in union with the Russian Federation, he would have another well of wealth and soldiers to draw upon.
Putin's mistake with Ukraine was his impatience. Putin's best strategy is to weaken each E.U. and N.A.T.O country from within, and have elections bring pro-Putin regimes into power, and have those countries exit N.A.T.O. and the E.U.
Infiltration is Putin's and Xi's best strategy to bring other nations into their spheres if influence. Economic integration via trade and development agreements is another vector of infiltration. China is effectively using this strategy to gain access and influence to resources around the Indian Ocean.
Putin is pursuing an age-old Russian objective of obtaining access to warm water ports for its navy. One strategic objective Stalin was not able to achieve during his conquest of Warsaw Pact nations was the conquest of Denmark. The British made a point to deny Stalin access to and influence over Denmark. Having Denmark in the Soviet orbit would have been advantageous for Russia's Baltic fleet to gain access to the open Atlantic Ocean.
Russian history is key to understanding Putin's movtives and objectives in Europe. Why were Sweden and Finland so quick to join N.A.T.O.? Finland used to be in 'personal union' with the Russian Empire. Sweden was the nation Russia fought to get access to the Baltic Sea and acquire Finland.
Russia needs to expand its influence westward into Central and Western Europe to become a global power again.
