Towards the end of an almost-great career, which did not include his dream assignment as secretary of state, the late US diplomat Richard Holbrooke confided in his diary. "The question constantly arises," he wrote, after failing to win the ear of then President Barack Obama, "how long do you want to do this?"

The biography in which the quote appears, Our Man by George Packer, is meant as an elegy for the "American century".