What did the European countries forget to take into consideration when new borders were drawn for Middle East countries after World War I?

World War I completed the European takeover of the Ottoman Empire's territories in the Middle East, and the region's modern boundaries emerged ... That agreement was superceded by another which established a mandate system of French and British control, sanctioned by the new League of Nations. Writer Tarek Osman traces many of the current problems in the Middle East to the secret Sykes-Picot agreement of 1916 ... The map that the two men drew divided the land that had been under Ottoman rule since the early 16th Century into new countries - and relegated these political entities to two ...