In his new book on the US in Iraq, New Yorker writer George Packer calls the conflict “the Rashomon of wars” – one whose cause, like the brutal crime at the centre of the Japanese film, remains little understood despite multiple retellings.

“Why did the US invade Iraq?” he wrote. “It still isn’t possible to be sure – and this remains the most remarkable thing about the Iraq war.” Two and half years after the US launched the war, with more than 2,000 US soldiers killed and the monthly death toll still rising, questions over how and why the US went to war are again roiling Washington.