Now that the Soviet Union has fallen, we need to ask what the purpose of NATO is.
Is it just an anti-Russian alliance?
If so, you can understand why Russia was concerned with NATO slowly expanding eastward.
We might say “NATO would never attack Russia”, but Russia has a long history of being attacked by its neighbors to the west. I don’t just mean WWI & WWII, I mean going back hundreds of years. It has happened over and over and over again. It’s not surprising they are paranoid about it.
NATO is attacking Russia as we speak. Those aren't Ukraine HIMARS and ATACMS hitting Russian cities and airbases.
Imagine if Mexico were launching Chinese missiles on Tinker or Ellsworth airbases, or on Omaha Nebraska, while they attempted to get back Texas.