The Ottoman sultans reigned for more than 600 years. In that time, they conquered almost all of what we consider to be the Middle East today, as well as North Africa, parts of East Africa and Southeastern Europe. But over the course of the 19th century, their power waned, and the beleaguered empire finally collapsed after a bitter defeat in World War I. Their fall created the Middle East as we know it today: It opened the region to European colonialism, invigorated nationalism and ended the spiritual leadership of the caliphate. But one cannot understand why the empire’s fall was so consequential — why an Ottomanless Middle East was such a big deal — without understanding how the Ottomans made their mark in the first place. Professor Marc David Baer is a historian at the London School of Economics and the author of “The Ottomans: Khans, Caesars, and Caliphs.” For this third installment of our series on the empire’s fall, he joins New Lines Magazine's Faisal Al Yafai to explore the Ottoman world that was lost, for better or for worse, 100 years ago. Produced by Joshua Martin