Assuming you're not reading this on your yacht, then the most contentious thing in the world is right beneath you.

Since the dawn of agriculture, peasants, farmers, landlords, and states have vied for control of the land.

Jo Guldi is the author of the The Long Land War: The Global Struggle for Occupancy Rights.

She spoke to Eleanor Penny about the history of that struggle, and how the struggle over the most basic condition of life is evolving now.