in Iraq, it was the Pax Saddam; he brokered no trouble from anyone in his country so any descent or inter-community violence was quickly quashed. After he was deposed, the Christians became easy targets for Islamic (peace and Love)anti-Christian violence. Since specifically protecting the small and weak Christian communities by us would be viewed as evidence of a crusade rather than a secular war of liberation by both the common Muslim and our Arab masters, our forces have not spent a whole lot of time and effort to protect them as they would any other obvious target of value.
I think farmer18th identified one of the problems, which is that the current Iraqi constitution - approved by us - enshrines Islam (and sharia). This means that while the great majority of Iraqis probably do not want an Islamic state ala Iran, the nutbags who do want such a state feel that their hopes are alive because the current Iraqi constitution does not discourage it. This, I think, is one of the reasons the two Islamic factions are still slugging it out, and one of the reasons Christians are being aggressively targeted by both of these groups.
We would have been much better off (and so would the Iraqis) if we had insisted on a secular, religiously neutral constitution. There’s a toleration clause in the Iraqi constitution, but since the document starts off by declaring the primacy of Islam, that’s pretty meaningless.