Part of the problem is the tribal nature of the region among Sunni, Shia, Wahabi etc.
And Iraq and Syria are what I’d call modern partitions. You see after World War I the Ottoman empire collapsed. I know this from reading T.E. Lawrence’s “The Seven Pillars of Wisdom”. The Ottoman Turks were pussies compared to the British lead expeditions. Seems the British learned a thing or two from their time in America.
Anyhow prior to the end of WW I Iraq and Syria did not exist. They were part of the Turkish or Ottoman empire.
It was the British who carved it all up and gave us the modern day nations. It takes a brutal dictator to keep a country together. And we’ve managed to take out one in Iraq and severely weaken one in Syria.
So that’s why it’s such a mess.