The intervention against Serbia and specifically the creation of Kosovo tend the western interventions to be raised by actual Russian experts as being a part of Russias thinking but even then they would emphasise this is wildly simplified. Russia under Putin and his cronies has been a constant evolution largely driven by internal Russian dynamics. The Orange, Rose and Euromaidan revolutions likely played far far larger roles in the minds of those in power in Russia.
If anything the real event that sparked all this was the Ukrainians pushing for membership of the EU. Putin and his entourage could not face a Ukrainian becoming as wealthy as Poland.
As for legality of attacking civilian infrastructure, its a question of interpretation.
Since Russia’s grotesquely illegal invasion of Ukraine last February, experts have detailed the failures, incompetence, and savagery of its military. In that context, consider this disturbing new …
sites.duke.edu
The single most effective thing the western allies did in WW2 was destroy German fuel production facilities. That seriously German agriculture and came close to sparking a massive famine: but it led to the annihilation of its air power and a major contributor to the destruction of two entire army groups (Heeresgruppe Mitte in Bagration and Heeresgruppe B in Normandy). This does not mean every attack is justified, its a motivating example of the more extreme case to justify. You can easily show other cases that are not justified.
We live in a world denuded of nuance.