I believe it was purely for reasons of expansion. I don’t know exactly what our response should have been, but we need to at least acknowledge that Ukraine is defending their sovereignty and Putin/Russia are the aggressors. We should support them at least minimally.
It’s going to boil down to your definition of “justified”.
In my experience, almost all confrontations between nations comes down to resources or access to resources. In this case, I read an opinion article suggesting that Russia wanted access to the Black Sea for access to or less expensive transport of oil. I also read that Russia was displeased with Ukraine’s strenghtening alignment with the USA.
Another perspective is that Ukraine used to be part of the USSR and Putin, whose popularity was waning, wanted to “make Russia great again” by reuniting the USSR under Russia control.
Back to my original point, was it “justified”? Not in my opinion, but in the minds of some Russians, Ukraine is acting very “un-Russian” and so they must be put in their place or taught a lesson.
Another observation of mine is that countries continue to behave like toddlers in the sandbox. They don’t talk out their differences, they take the toy that they want, regardless of who has it and if things don’t go their way, they throw sand.
Yes, I do believe they feel justified
Controlling Crimea gives them a much better port than anything else around there, and a big naval base they developed around it.
A lot of the reasoning behind the Warsaw Pact back in Cold War days was a buffer zone. If WWIII did happen, they wanted to keep it far from their territory. Same deal. Now they imagine NATO right up on their border and that buffer zone is looking like a really good idea. In this scenario, they also have no reason to care whether that part of Ukraine is a bombed out wasteland