Answer:
European pressure was the main factor in the |800s.
Step-by-step explanation:
The decline of the Ottoman Empire - that once was close to conquer Viena - started already in the 18th century when Hungary passed to the Habsburg Empire. But it had to be the 19th century (the age of European Empires) to take reallly care of business. The European Imperialistic Empires started a vicious competition in gaining world power. One of the side effects was the further weakening of the Ottoman Empire. Though nobody wanted to make his hands dirty by putting the dagger into the heart of the Ottoman Empire, it was kept alive untill 1914. In the meantime ethnic groups or countries such as Macedonia, Bulgaria, Albania and Serbia defied the crumbling Ottoman Empire.