The sight of a river of empty red chairs running down the length of Marshal Tito Boulevard in Sarajevo, commemorating the 20th anniversary of the start of the siege of the Bosnian capital, has been poignant. Twenty years on from the beginning of the war in April 1992, a conflict that would go on to claim about 100,000 lives, more than 11,000 in Sarajevo – hence the red chairs, one per victim – it seems incredible that the West allowed it to happen in the first place.

What is more incredible still is that when the siege of the city started in the spring of 1992, the West did not act sooner to stop it. For the people of Sarajevo, then, this has been a chance to mourn and remember lost parents, brothers, sisters and children. For us in the rest of Europe, meanwhile, it is a depressing reminder of the fact that as a continent we were not able to act decisively even to stop shocking and flagrant atrocities from occurring right under our noses. Forget talk of far-off countries of which we know little. Bosnia was and is only a couple of hours' drive from Vienna.

One lesson to be drawn from that river of red chairs – the most obvious – is that we should not allow cities to be subjected to medieval-style sieges for three-and-a-half years. After years of dithering and claims that nothing could be done to stop the Bosnian Serbs and their paymasters in Belgrade, it turned out that a few judicious air strikes were almost all that was needed. Within weeks of those strikes, the various factions were hurrying to the negotiating table and the war in Bosnia was over. The peace that has followed may have been unsatisfactory in many ways, but at least there has been peace.

These days the idea of Liberal Interventionism, the notion that the West can and sometimes should intervene militarily in troubled parts of the world, is in retreat.

In the minds of many people it has been discredited beyond redemption by the disasters that followed the invasions of Afghanistan and Iraq. This feeling is understandable. Both conflicts serve as warnings of the perils of hubris. But as civilians continue to die in large numbers in Syria, Bosnia is a reminder that inaction and excessive caution are not always the right policy either.