First of all I'm not getting into this 'ownership' of territory. The squabbling goes back to when man first chucked a rock at other man and stole his stuff. Let's instead look at the protagonists.....
- Saudi Arabia
- Other Euro
- Other Arab
One of the key issues is the religious spread. Saddam never played the religion card, probably because he was in a minority and he wasn't exactly leading a deeply religious life-style.
Iraq has a Shia majority whom Saddam promised reforms if they helped with the war against Iran. They did and Saddam reneged on the deal. He then tried to 'eliminate' those whom he did the dirty on. He had other problems trying to finance the war so decided neighbours Kuwait should foot some of the bill as they were predominantly Sunnis. Naturally they refused to squander the wealth of the country on a pointless war so Saddam just took it anyway. This gave the west reason to engage Saddam with the reluctant blessing of other Arab states, and we all know what happened then.
Trump's comments about Obama 'creating' Daesh are probably correct, in that simply removing Saddam left a power void. A 'democratic' government was put in place but it was never going to work, commonsense dictates otherwise. The USA and allies may have gotten rid of Saddam but they never destroyed his army. Of course Saddam's loyal army were obviously Sunnis. Foreign troops filtered out of Iraq and the remnants of Saddam's army regrouped to form Daesh. Without Saddam and the excesses of his family at the fore, the struggle for control of resources went from political to religious.
This was a masterstroke because now the extremists could theoretically call on every Sunni Muslim to join the fight or be a traitor to their religious order. It was - and to a degree still is - effective to curry favour among other Sunni nations. Saudi Arabia seem to be showing a marked reluctance to condemn Daesh and Turkey take the view that they don't want to attack those who are busy killing their enemies i.e. the Kurds.
Syria obviously have the problem where the people want the Assad dictatorship to fall but he is backed by the Russians which is bad news for Israel as there is still disputed territory with Syria around the Sea of Galilee, and the Golan Heights where, guess what? Oil has been discovered. That is without even taking the Palestine affair into consideration. This is in turn making the USA 'twitchy' because Israel are a valued ally in the region.
The USA could have finished the war by now but in the cause of democracy feel it is better just to assist and let Iraqi's take back Iraq. There is very good reason for this politically but what is the humanitarian cost? With every day that passes there are more atrocities, more suffering of innocents, just because of politics.
I might be wrong, I don't know. On this basis though, those in power of the countries above are directly responsible for prolonging the suffering.