The Fall of the Ottomans by Eugene Rogan (Basic Books) provides a vivid account as to the origins of the current turmoil in the Middle East. The Ottoman Empire was established in the Sixteenth Century and extended from south of Vienna to include the Balkans, Turkey, Syria, Lebanon, Palestine, Egypt, and all the way around the Mediterranean up to Algeria.
Fearing encroachment of the Russians on Turkey’s northern flank, the Ottomans formed a military alliance with Germany. Two years into WWI, Britain, and France were bogged down in the killing fields of the Western Front. To divert German resources, the Allies attacked the Ottoman Empire by landing troops in Gallipoli–a devastating defeat. The Allies further attacked the Turks up the Euphrates to Bagdad, at the same time Colonial Lawrence led the Arab armies north from Egypt to Damascus, with the promise that they were being given their independence. Instead, the British and the French became colonial powers, dividing the defeated Ottomans according to the Sykes-Picot secret agreement.
These new borders, drawn in straight lines, brought Iraq, Transjordan, and Palestine under British influence, and Syria and Lebanon under French influence. The newly created borders did not correspond to actual sectarian, tribal, or ethnic distinctions on the ground, leading to the present-day conflict.