In comparison to the state of things in Iraq now, they did work. The problem is that the American public(rightly so) were tired of the decade+ long wars and wanted the troops home, so we pulled out. As we saw, the Iraqi military still wasn't able to stand on its own legs against a relatively organized and well-equipped guerilla force.

If Iraq had a fully capable military(instead of the partially capable one they have now), ISIS would never have spread into the country. For all the problems the US and its allies created in Iraq, the country was comparatively much more stable, and for the most part people got on with their lives.

They work but there has to be a commitment to seeing things through no matter the extent of the ensuing carnage, something most western countries have lost their stomach for. See: Chechnya.