Putin did not have to convince anyone there that Ukrainians (and other neighbor countries) don’t have the right to exist as an independent nation.

This is absolutely not true. Many Russians have relatives in the countries which were formerly part of the Soviet Union. There have been many protests within Russia against the war, which were usually met with violent suppression. Many in opposition of the war fled if they were able to.

But I guess Russians just really want to fight against their foreign relatives, simply because they themselves are Russian.

there is a national identity that they have had for decades and centuries

Yeah, there was this one guy who was in power for like 24 years who was a part of the intelligence community before he became a politician. Before he came to power, the entire world wanted the nation gone (and still do). Crazy how having every western government hate you could be used to create a national identity.

for understanding just how much of the responsibility for the war falls on the nation and not just Putin.

If the Russian people are responsible, I guess we should start bombing Russian cities then. That sounds reasonable.