I believe the answer is A, World War 1 was the main cause of the ottoman empire to break up, and that caused political unrest. But please check on some history websites to make sure it's correct :)
Back then in 1914 The Ottoman Empire entered the First World War due to the alliances with the Central Powers.
The end of WWI by 1919 meant the Turkish War of Independence which lasted from 1919 to 1923. Furthermore, the French together with the British authorities had made a pact to share the Ottoman Empire domain by fostering revolts between the Ottoman Arabs and their Turkish government.
These two factors caused the disintegration of this vast empire and the formation of the Turkish Republic.
It went from controlling a powerful empire to forming an independent republic. (APEX 2018)