The best 'documentations' about the backgrounds of the modern-day Syria are two recently published books:

- A line in the Sand
Britain, France and the Struggle that Shaped the Middle East
by James Barr

- The Great Syrian Revolt
And the Rise of Arab Nationalism
by Michael Provence

Both are based on original, official documentation from those times. The first is using this to explain the Sykes-Picot agreement, and then map the subsequent developments in the Middle East, all of which were casued by the same. The second book is mapping the situation in Syria during the first years of French mandate.

After reading them, I would recommend such lecture like
- War in the Desert and
- The Story of the Arab Legion
by Glubb Pasha

for understanding 'details' of problems for locals caused by Sykes-Picot agreement (surely, in the case of these books, it's foremost the 'coming into being' of Iraq and Jordan that is described; this is where the British did better than the French in Syria, even for the same, entirely wrong, reasons). Finally, after all of that, get

- Taking Sides and
- Living by the Sword
by Stephen Green, for understanding how the US governments did their best to follow in the wake of the British and French...