Nineveh fell in 612 BCE to a coalition of Medes and Babylonians, and the Assyrian state ended within a few years. What did not end was habitation. The northern Mesopotamian heartland around Mosul, the Nineveh plain, Tur Abdin and the Hakkari mountains remained populated, and from the early centuries of the common era that population was substantially Christian, in the Church of the East and later also the Syriac Orthodox Church, using Syriac as its liturgical language.
Christoph Baumer's history traces that church from its Persian base across Asia, along the Silk Road to Tang China and into India, at one point covering a wider geography than any other church of its era, before contraction under the Mongol and Timurid periods left it concentrated again in its homeland.
Whether the modern Assyrians descend from the ancient ones is a question with both a scholarly literature and a political charge, and the atlas does not settle it. The name was taken up as a national designation in the nineteenth and early twentieth centuries, in the same period that produced the massacres of the First World War and the flight from Hakkari. The community today is largely diasporic, its remaining Iraqi and Syrian populations reduced further by the events following 2003 and by the occupation of the Nineveh plain in 2014.