In his column (12 September) in favour of intervention, David Blair confines himself  to the events in Syria from the onset of the civil war in 2011. He writes as if we had not recently intervened elsewhere, nor learned anything from doing so. We invaded Iraq and brought disaster. We invaded Afghanistan and brought a new kind of chaos. We helped destroy Gaddafi by air attacks, but his fall produced  a predictable anarchy and banditry, making normal life impossible. It has also spread weapons from Libya throughout the region to add to those sold by rich arms-trading nations. Had these actions not failed so badly, then Blair's  case might appear to have some sense. The main lessons that we have learned from these three responses are that military intervention, as we hav