Russia and the Ukraine
Whatever you think of the merits of the case (laid out in heroic detail by Wikipedia), you have to pity the Russians a little bit. For centuries the biggest country in the world, Russia could never conquer its way to a single economically useful land border or seaport. What used to be a comfortable ring of client states (the 'near abroad', in Russian terms) went away with the fall of Communism, and now the former heartland of the Soviet Union is getting all up in Russia's business and demanding to be treated like a sovereign state, instead of remaining a complacent little throw pillow like Belarus. The Russians react to this a bit like the Americans might if the Midwest were to secede, begin speaking French, and demand boxcars full of quality merchandise at low, low prices. It really burns them up.
