Answer:
Other countries deliberately weakened it.
The ambition of European powers also helped to hasten the Ottoman Empire’s demise, explains Eugene Rogan, director of the Middle East Centre at St. Antony’s College, Oxford. Russia and Austria both supported rebellious nationalists in the Balkans to further their own influence. And the British and the French were eager to carve away territory controlled by the Ottoman Empire in the Middle East and North Africa.
It faced a destructive rivalry with Russia.
Neighboring Czarist Russia, whose sprawling realm included Muslims as well, developed into an increasingly bitter rival. “The Russian empire was the single greatest threat to the Ottoman empire, and it was a truly existential threat,” Reynolds says. When the two empires took opposite sides in World War I, though, the Russians ended up collapsing first, in part because of the Ottoman forces prevented Russia from getting supplies from Europe via the Black Sea. Tzar Nicholas II and his foreign minister, Sergei Sazanov, resisted the idea of negotiating a separate peace with the empire, which might have saved Russia.