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The Serbian revolution (1804–1815) marked the beginning of an era of national awakening in the Balkans during the Eastern Question. Suzerainty of Serbia as a hereditary monarchy under its own dynasty was acknowledged de jure in 1830. In 1821, the Greeks declared war on the Sultan. A rebellion that originated in Moldavia as a diversion was followed by the main revolution in the Peloponnese, which, along with the northern part of the Gulf of Corinth, became the first parts of the Ottoman Empire to achieve independence (in 1829). By the mid-19th century, the Ottoman Empire was called the "sick man" by Europeans. The suzerain states – the Principality of Serbia, Wallachia, Moldavia and Montenegro – moved towards de jure independence during the 1860s and 1870s.
What did Europeans refer to the Ottoman empire as in the 19th century?
the "sick man"