I am using the word Rus as shorthand to describe collectively Ukraine (the heart of ‘Old Rus’), Belarus (‘White Rus’) and of course Russia itself. I have extended Old Rus (Stary Rus) to include modern Ukraine in the south, because we are not in the 13th century any more, and peoples and borders shift. For pragmatic reasons that includes Crimea, even though it was not historically part of Rus.
Rus is at the moment a particularly loaded word, during the confrontation between Ukraine and Russia, because it is an idea that is being used by Putin's Russia to imply some kind of claim over Ukraine. Ukraine is a separate country, with its own traditions and aspirations and I am using the word Rus only as a convenient shorthand to describe collectively the three countries of Ukraine, Russia and Belarus and to explore their common heritage, as well as their very important differences. But Rus does not exist any more, certainly not as a nation-state.
The ethnic, political and historical make-up of the region is complex. Many of the writers we think of as the well known 'Russian' writers are actually Ukrainian, like Gogol, Bulgakov, Grossman, and Nadezhda Mandelstam all of whom I refer to extensively in my essays. And aside from Russians and Ukrainians, there were the Poles, the Tartars, the Jews, the Circassians, the Greeks and Scythian descendants and many other nationalities, all of whom help to define the region today. Nowhere is this more so than in Crimea, which until their deportation during the Russian empire belonged above all to the Tartars, but was an unprecedented crossroads for different nationalities.