Russia acknowledged Ukraine in its borders as independent state, and these claims by Putin are lawless. To justify it by ownership back in history is absurd, since every piece of land in Europe has been in many states even over the last 2 centuries, and anyone could claim anything.
In reality, these are mere excuses, the real reason is post-imperial resentment. In 1989 the USSR, broadly speaking, lost the Cold war, and in new year 1992 collapsed. That event is what many want to take revenge for.
But it wasn't always like that. I remember late 80s, when most of the common people were fed up with the communist party and excited of possible friendship with the West. I remember common people, who weren't political dissidents at all, bemoan the regime all the time in 1988 and later. (Here's a
good book with the study what people felt, based on diaries.) Only a few very ideologized people tried to defend the Soviet Union. Even the secret services did nothing. People were tired of communists and waited something new to happen.
Then came the crisis of the 1990s. I remember January 1st of 1992 when the prices in our city shops doubled, and then they doubled again 2 months later. Inflation in 1992 alone was 25x. Then many state enterprises and research institutes laid off personell, in some places there wasn't any cash to pay the wages for months. The crisis magnitude was -40% GDP/cap, and was a cold shower. I guess this is when many started feeling resentful, and the final turning point was the war in Yugoslavia in 1999. It made many turn around in their opinions. Those who had bemoaned the USSR, started to think it was a good country destroyed by some conspiracy. The ruling elites seem to share this resentment fully.
If stopping NATO were a goal (though our military generals who dare to speak, don't think it's a real threat), then Putin failed.
In early 2000s, state media would mention every once in a while an unfriendly symbolic move from Eastern Europe - a painted monument, a removed monument, an anti-Russian protest, and so on. Our state responded offencively, and things went in a downward spiral over the 20 years.
When you're told that "ours" are attacked somewhere "there", it's easy to take "ours" side. Maybe it was LFS that made me friends with a guy from Ukraine. We tested mods in 2004 and discovered that you could make bike (though we didn't change the XFG body). The guy made a video with a rock song about a scary biker, in Ukranian, from which I followed to listen to songs, read their media. Maybe this made me look at them from a different angle.
Another personal story: in 2003 I got the first bank card in my life. There was only one bank I knew that made them rather cheaply, and it took an hour by bus and subway, and a long walk in -15°C to get there, but I wanted an S1 licence that it didn't matter. And still there were some issues with payments, because there were few real buyers from Russia, and lots of fraudsters, and I hoped we'd become a friendlier and more opened country. Seems that in the coming years this process will go backwards. What a shame.