The Assyrian homeland or Assyria refers to a geographic and cultural region situated in Northern Mesopotamia that has been traditionally inhabited by Assyrian people. The areas that form the Assyrian homeland are parts of present-day northern Iraq, southeastern Turkey, northwestern Iran and, more recently, northeastern Syria. Moreover, the area that had the greatest concentration of Assyrians in the world until recently, is located in the Assyrian Triangle, a region which comprises the Nineveh plains, southern Hakkari and the Barwari regions. This is where some Assyrian groups seek to create an independent nation state.
Middle Ages
Both Syriac Christianity and the Eastern Aramaic language came under pressure following the Arab Islamic conquest of Mesopotamia in the 7th century, and Assyrian Christians throughout the Middle Ages were subjected to Arabizing superstrate influence. The Assyrians suffered a significant persecution with the religiously motivated large scale massacres conducted by the Muslim Turco-Mongol ruler Tamurlane in the 14th century AD. It was from this time that the ancient city of Assur was abandoned by Assyrians, and Assyrians were reduced to a minority within their ancient homeland.  A Schism occurred in 1552 AD, when a number of Assyrian Christians entered communion with the Roman Catholic Church, which, after initially naming their new followers The Church of Assyria and Mosul, coined the term Chaldean Catholic in 1683 AD, giving rise to the modern Chaldean Catholic Church by 1830 AD. This term is purely theological however, the Assyrian Chaldean Catholics having no historical, ethnic, cultural or geographic link to the ancient inhabitants of Chaldea in south east Mesopotamia, who had disappeared into the native population of Babylonia by the 6th century BC.  Upper Mesopotamia had an established structure of dioceses by AD 500 following the introduction of Christianity from the 1st to 3rd centuries AD. After the fall of the Neo Assyrian Empire by 605 BC Assyria remained an entity for over 1200 years under Babylonian, Achamaenid Persian, Seleucid Greek, Parthian, Roman and Sassanid Persian rule. It was only after the Arab-Islamic conquest of the second half of the 7th century AD that Assyria as a named region was dissolved.  The mountainous region of the Assyrian homeland, Barwari, was part of the diocese of Beth Nuhadra (current day Dohuk) since antiquities and have seen a mass migration of Nestorians after the fall of Baghdad in 1258 and Timurlane's invasion from central Iraq. Its Christian inhabitants were little affected by the Ottoman conquests, however starting from the 19th century Kurdish Emirs sought to expand their territories at their expense. In the 1830s Muhammad Rawanduzi, the Emir of Soran, tried to forcibly add the region to his dominion pillaging many Assyrian villages. Bedr Khan Beg of Bohtan renewed attacks on the region in the 1840s, killing tens of thousands of Assyrians in Barwari and Hakkari before being ultimately defeated by the Ottomans.

Q: Who ruled over the Assyrian homeland in the middle ages ?
A: Muslim Turco-Mongol ruler Tamurlane

Q: Who did he have to defeat to rule over this land ?
A: The Assyrians suffered a significant persecution with the religiously motivated large scale massacres
Who else ruled the region during the middle ages ?
The Church of Assyria and Mosul,
The Church of Assyria and Mosul,