The headlines are dominated by regional crises – in Ukraine, in Iraq and in the South China Sea. But is there a common thread that ties together these apparently unconnected events?

One global theory is advanced by Walter Russell Mead, a professor at Bard College, in a recent piece for Foreign Affairs, entitled “The Return of Geopolitics”. Prof Mead’s piece, together with a rejoinder by Professor John Ikenberry of Princeton University, offers a way of thinking through current patterns in world politics.

The shape of the world order that emerged after the collapse of the Soviet Union is fairly easy to define. Its key characteristics included a globalised economic system, functioning multilateral institutions and – most important of all – an unchallenged role for the US as the most powerful player.