So what was the basis of this war from Putin's perspective?
There are the reasons Putin gave and the reasons that are rational from a geopolitical point of view.
I recommend listening to Peter Zeihan's appearance on Joe Rogan's podcast but on a nutshell:
Securing a crucial flank against Nato, turning Ukraine into a buffer zone like it has been for ages (obviously)
An aged, diseased population that has been seriously shrinking for decades meaning they must absorb other populations to solve their demographic problems (hence the massive abductions of Ukrainian children). Without this, Russia is finished as a country by 2070 at the latest without a single shot fired due to total demographic collapse. 2022 (according to Zeihan, always) is the last year they had enough males in their 20s to even attempt an invasion.
Denying Ukraine the massive undeveloped energy resources of the Black Sea ensuring they will never compromise Russian's status as an energy superpower.
Russian farmland being among the least fertile, worst connected space in the world (roads are in terrible shape, they mostly have rail), so grabbing Ukraine's farmland is a massive boost.