ANSWER: The end of World War and the defeated Central Powers, in which The Ottoman Empire was part of.
By the time The Ottoman Empire surrendered in the World War I, its power had been declining for centuries. It had several economic problems, was facing too many competition in the trade business, high unemployment rate, a weakening of its centralized power, the rise of nationalist movements, Turkish uprisings etc.
At the end of the World War I, The Ottoman Empire ended up signing an Armistice of Mudros, (Oct. 30, 1918), between Great Britain (representing the Allied powers), which marked its defeat.
After that, the empire was forced to sign a series of agreements in which he gave up his lands and forced its disintegration into numerous territories, and Turkey became its immediate successor.
Finally, the Treaty of Sèvres, signed on Aug. 10, 1920, between the Allied powers and representatives of the government of Ottoman Turkey, completely abolished the Ottoman Empire.
