...It's not like they ever lost it, really. They're fighting to keep the status quo, but sice most of the status quo was unnoficial since Hruscev, it looks rather shocking. Technicaly, it's not really an invasion as much as dropping the PR pretenses about how things actually worked over there.
Technicaly it is.
http://en.wikipedia.org/wiki/Budapest_Memorandum
Yes.
All territory on earth has at some point had another national identity than what it has today, wether it belonged to a neighboring country - or it enjoyed independence in early history. Like I once told a grumpy old white-pride guy, that if we're gonna be picking and choosing what historical "basis" we "belong to", we should just go all the way back. "Proud white Europeans" should worship bears, and dance around fireplaces and stuff like that. Count me out, I got things to do.
Same with Crimea - it belonged to Russia, it no longer does, they traded it for a huge stockpile of nukes, they shook hands, signed the paper, and sealed the deal. Coming back to cry about it is lame. Also, come on, Russia should ask Finland what their opinion is, about lost land, stolen land, taken land, land not given back, false pretexts, etc, I bet the Finns could elaborate a bit on the problem.