ISIS, contrary to what happens with Al-Qaeda, was mainly anti-Shiite and not anti-American. The reason is that Turkey has a lot of influence over ISIS, while many Saudis are behind Al-Qaeda. And the Turkish geopolitical interests are much closer to the American ones, at least when compared to the Saudi ones. I do not mean to say that only Turks are behind ISIS. But Turkey is the strongest Muslim country in the world in military terms.
However the problem is that in Syria, American interests are much closer to the interests of the socialist Sunnis of Syria and of the Syrian Kurds, and in Iraq they are much closer to the interests of the Iraqi Shiites and the Iraqi Kurds. Turkey on the other hand, together with the Arabs of the Persian Gulf, in Syria and Iraq they support the Islamist Sunnis i.e. ISIS, and other Sunni Islamist organizations. Therefore the Americans and the Turks support opposing sides in Syria and Iraq.
As you can read at the following International Business Times article, there is fear that ISIS was behind yesterday’s mass executions in California (December 2nd 2015). It remains to be seen whether the attacks were carried out by ISIS sympathizers, as was the case with the attacks of Charlie Hebdo in Paris (January 2015), or whether the attacks were carried out by ISIS itself, as was the case with the attacks of Paris in November 2015.
It is also difficult to distinguish between ISIS and Al-Qaeda, because sometimes the members of ISIS join Al-Qaeda and vice versa, depending on who is paying better. I would expect that in Syria and Iraq, where ISIS is very strong, and Turkey is very strong too, it is the members of Al-Qaeda who join ISIS most of the time, and in Africa, where Turkey’s presence is not equally strong, and where Al-Qaeda is very well organized, it is ISIS members who normally join Al-Qaeda. Actually it is not as simple as that, because we saw Boko Haram, the terrorist organization of Nigeria, changing its name and becoming the ISIS branch of Nigeria. I am just saying what would make more sense, but it is not necessarily correct.
For the IBT article see:
“Islamic State In California? After San Bernardino Shooting, Rumors Abound Online About Potential ISIS Connection”, December 2015