sentences:  By the 19th century, Eastern Armenia had been conquered by the Russian Empire, while most of the western parts of the traditional Armenian homeland remained under Ottoman rule.During World War I, 1.5 million Armenians living in their ancestral lands in the Ottoman Empire were systematically exterminated in the Armenian Genocide.In 1918, following the Russian Revolution, all non-Russian countries declared their independence after the Russian Empire ceased to exist, leading to the establishment of the First Republic of Armenia.