Frequently, you will hear claims of Russia being right to invade Ukraine due to NATO expanding east. There may be a gram of truth to this, but ever since Putin took control, he has been trying to claw back territory lost when the Soviet Union broke apart. I point to these examples.
https://en.wikipedia.org/wiki/Transnistria
https://en.wikipedia.org/wiki/Abkhazia
https://en.wikipedia.org/wiki/Chechnya
Yet Poland, Lithuania and Germany let Russia keep the Kaliningrad Oblast.