Should the west arm the Syrian rebels? That is the issue of the day in Washington, London and at the Group of Eight summit. But behind this debate lies a bigger question. Can western powers continue to shape the future of the Middle East as they have for the past century?

The current, increasingly fragile borders of the Middle East are, to a large extent, the product of some lines on the map drawn by Britain and France in the Sykes-Picot agreement of 1916. The era when Britain and France were the dominant outside powers ended definitively with the Suez crisis of 1956 – when the US pulled the plug on the two nations’ intervention in Egypt. During the cold war, the US and the USSR were the big players. After the collapse of the Soviet Union in 1991, America stood alone as the great power in the Middle East: organising the coalition to defeat Saddam Hussein in 1991, protecting the flow of oil from the Gulf, containing Iran and attempting to broker a peace settlement between Israel and the Arab states.

Those who are urging the US to get more deeply involved in the Syrian conflict now are living in the past. They assume that America can and should continue to dominate the politics of the Middle East. But four fundamental changes make it no longer realistic, or even desirable, for the US to dominate the region in the old way.