And if so, is it exaggerated? I've read quite a lot of books about the Ottoman Empire and none of them mentions it. The only book that describe it as a genocide/massacre is "The Fall of The Ottomans" by Eugene Rogan, and In "The Encyclopedia of Ottoman Empire" it's said that they were indeed attacked, but most of them survived and later fled Turkey (So it's not a massacre or genocide)
Yes, the Assyrian genocide is "real". In fact, the term genocide was coined to describe the systematic murder of Assyrians, Armenians, and Anatolian Greeks by the Ottoman Empire leading up to and during the First World War. An entire population does not need to perish for it to be genocide- genocide is mass murder with the intent of destroying an ethnic group; this certainly qualifies.
Very briefly, you must understand the context of Assyrian-Turk relations at the time, The peoples of ancient Assyria, among others, inhabited Asia Minor for over 2000 years; eventually, they became part of a succession of empires, including the Macedonian Empire, the Sassanid Empire, and the Byzantine Empire. During the 7th century, Muslim conquers captured Asia minor and Mesopotamia from the Sassanids and the Byzantines. Some of the first Christians, the Armenians, Assyrians, and Greeks became second-class citizens in the new Islamic civilization. Overtaxed, persecuted, and possessing few rights, the Assyrians held little but contempt for their Ottoman rulers. European powers. especially Russia, began to pressure the Ottomans to improve conditions for these groups during the mid 19th century; the oppressed Christian minorities saw the Europeans as fellow Christians and protectors.
Occasional Massacres of Assyrian villages preceded the First World War. When the war broke out, the Young Turk Government declared the Christians potential collaborators. Armenians, and Assyrians alongside them, were massacred by the thousands by the army, as well as local groups. Forced to flee East, many of the Assyrians who were not killed by hunger. disease, and exposure were hunted by armed Arab and Kurdish fighters. out of the 600,000 Assyrians living in the Ottoman Empire at the beginning of WWI (the vast majority of Assyrians), around 300,000 died, nearly half of the Assyrian population.