Still in Books and Arts; Book Review;Foreign interventions;When to hold and when to fold;

Rory Stewart and Gerald Knaus are well placed to pose and answer these questions. Before Mr Stewart became a Conservative MP, he was a deputy governor of two Iraqi provinces. He also walked across Afghanistan and wrote a bestseller about the experience. Mr Knaus, a political economist, runs the European Stability Initiative, a Berlin-based think-tank founded in Sarajevo in 1999, which has been particularly influential in the Balkans.

The book is structured as two essays with a lengthy joint introduction. Mr Stewart has written a colourful account of his time in Afghanistan and his failed attempts to stop what he sees as a self- defeating build-up of ambitions, troops and plans. He skewers gobbledygook notions of bringing Afghans accountable governance and Western-style rule of law. It is not that he is against such things, but that he doubts the ability of foreigners to impose it all. He cites a pragmatic admonition from English Mountain Rescue: “Be prepared to turn back if conditions turn against you.”

Writing about Bosnia, Mr Knaus deploys heavy artillery in arguments that he has made before. Intervention there has been a stunning success, he says, given the state of Bosnia at the end of its devastating war in 1995. Hundreds of thousands of refugees have returned, not a single intervening soldier was killed (after the war), and today's problems are of the conventional political sort, not the kind that herald another war. Not only does Bosnia enjoy free and fair elections, but also it has relatively little crime. Mr Knaus argues that the only missteps came from assumptions held by those like Lord Ashdown, when he was de facto governor of Bosnia, that well-meaning envoys could behave like imperial viceroys, sacking elected yet obstructive leaders at will.

From rather successful interventions, defined as Bosnia and Kosovo, the authors convey an important lesson: that is, the experience garnered in one place is generally not much use elsewhere. Bosnia was a success because the intervention came as part of the 1995 Dayton peace agreement, which ended the war and which all the exhausted sides committed themselves to. In Kosovo the vast majority of its people—ethnic Albanians, nearly all of them Muslims—were very grateful for what they saw as their America-led liberation from the Serbs. Mr Knaus also argues that the United Nations war-crimes tribunal was vital as a form of closure and for removing from the political scene characters such as Ratko Mladic, a Bosnian Serb general now on trial for genocide in The Hague.

So, does intervention work? As any Bosnian peasant may tell you, “maybe yes, maybe no.” It depends on the circumstances and requires modest ambitions. Muddle through with a sense of purpose, says Mr Knaus. Do what you can, where you can and no more, agrees Mr Stewart. In policy terms that sounds a bit like “yes” to Libya, “no” to Syria and so on.