First, it was secret without any Arabic knowledge, and it negated the main promise that Britain had made to the Arabs in the 1910s - that if they rebelled against the Ottomans, the fall of that empire would bring them independence.
When that independence did not materialise after World War One, and as these colonial powers, in the 1920s, 30s and 40s, continued to exert immense influence over the Arab world, the thrust of Arab politics - in North Africa and in the eastern Mediterranean - gradually but decisively shifted from building liberal constitutional governance systems (as Egypt, Syria, and Iraq had witnessed in the early decades of the 20th Century) to assertive nationalism whose main objective was getting rid of the colonialists and the ruling systems that worked with them.
This was a key factor behind the rise of the militarist regimes that had come to dominate many Arab countries from the 1950s until the 2011 Arab uprisings.
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The second problem lay in the tendency to draw straight lines. [...] That meant the newly created borders did not correspond to the actual sectarian, tribal, or ethnic distinctions on the ground.