My two cents; If you look past the false rhetoric meant to galvanize the population it is about the ability to maintain coercive influence over their neighbors for economic reasons. To do this they employ intimidation and if all else fails military force. Russia is run like a mob crime family where the oligarchs appeal to Putin to solve their business/economic issues using the power of the state and they presumably give him a cut of the profits which is where his reportedly vast secret wealth comes from. Ukraine becoming closer to the EU economically over the past 10 years is what this is ultimately about.

People saying this is mostly about NATO expansion are missing the real issue. NATO aspirations are symptom not the cause of the dispute. If a country is in NATO it limits the means Russia has to coerce them. ie: it takes military intervention off the table since they would not be picking a fight with only one country but the alliance.