Also, not just individual ownership of land, but the vastly unequal amounts of land the countries have, proportionally to their population.
Yes, I know that often, a lot of the land isn't ideal for habitation (although human ingenuity seems to know no bounds); but who originally decided that - just for one - Russia should have 11% of the world's land for less than 2% of the population? Yes, I know, the answer is most probably 'a lot of war, starting a long time ago'...