I'm pretty sure that Putin literally believes all that tripe about "triune people", and I don't think he needed any excuses beyond that. Well, there's also the part where I think he really wants to end up in the history textbooks with the same standing as Ivan III and other famous "gatherers of the land".

So, in a sense, he is also fighting for his country and its nation - it just happens to be an imaginary one: "Greater Russia".