The Ottoman Empire was founded of the Byzantine Empire. The emperor Constantine turned the late capital of the Byzantine Empire, Byzantium, to Constiantonople and thus the Ottoman Empire was formed in roughly 1299. The Ottoman Empire was a successful empire for awhile, but was severely weakened after losing the Battle of Lepanto to the Spanish of 1571. The Ottoman Empire continued to lose it's territorial expansion and became known as the "sick child of Europe."
However when Russia tried to invade and take over, western European powers united to defeat Russia and keep the Ottoman Empire as a middle-man in trade and reduce the power of Russia. The Ottoman Empire fell during World War 1 when it chose the losing side.