I go into that question in my recent "chess piece" Donbas is filled with a large Russian speaking / identifying population. They wanted to succeed, and Putin helped them do it with the "little green men". (How much of population there really wanted it is unknown, like all things) Strategically speaking, the Donbas has trivial importance. But it's the only place Russia has a foothold. It drives me nuts most news does not point out that simple fact.