ISIS is just the remnants of the Saddam regime that scampered into Syria ahead of the US armed forces in 2003. They laid in wait until we eventually pulled out of Iraq and now we are seeing the results.
I don’t really think that’s true. Saddam, for all his flaws, was a pretty secular guy. He had Christians in his government in high positions.
He protected Christians and Yezidis against Islamists, as part of the standard dictator practice of divide and conquer. Since the majority of his population was Shia, he stomped all over them and was by comparison less harsh on Christians, Yezidis and Sunnis. Kurds were a special case.
This is, BTW, exactly the same as Assad’s policy in Syria. You are comparatively less harsh on minorities, because they don’t threaten your power in the same way the majority does.
An interesting side effect of this policy is that when the majority comes to power, it views the minorities as having been supporters of the dictator, which they often were. So they then take their revenge.