Assyria was the region in the Near East which, under the Neo-Assyrian Empire, reached from Mesopotamia (modern-day Iraq) through Asia Minor (modern Turkey) and down through Egypt. The empire began modestly at the city of Ashur (known as Subartu to the Sumerians), located in Mesopotamia north-east of Babylon, where merchants who traded in Anatolia became increasingly wealthy, and that affluence allowed for the growth and prosperity of the city.
According to one interpretation of passages in the biblical Book of Genesis, Ashur was founded by a man named Ashur son of Shem, son of Noah, after the Great Flood, who then went on to found the other important Assyrian cities. A more likely account is that the city was named Ashur after the deity of that name sometime in the 3rd millennium BCE; the same god's name is the origin for `Assyria'. The biblical version of the origin of Ashur appears later in the historical record after the Assyrians had accepted Christianity, and so it is thought to be a re-interpretation of their early history which was more in keeping with their belief system.
The Assyrians were a Semitic people who originally spoke and wrote Akkadian before the easier to use Aramaic language became more popular.
Historians have divided the rise and fall of the Assyrian Empire into three periods: The Old Kingdom, The Middle Empire, and The Late Empire (also known as the Neo-Assyrian Empire), although it should be noted that Assyrian history continued on past that point, and there are still Assyrians living in the regions of Iran and Iraq, and elsewhere, in the present day. The Assyrian Empire is considered the greatest of the Mesopotamian empires due to its expanse and the development of the bureaucracy and military strategies which allowed it to grow and flourish.

THE OLD KINGDOM

Although the city of Ashur existed from the 3rd millennium BCE, the extant ruins of that city date to 1900 BCE which is now considered the date the city was founded. According to early inscriptions, the first king was Tudiya, and those who followed him were known as “kings who lived in tents” suggesting a pastoral, rather than urban, community. Ashur was certainly an important centre of commerce even at this time, however, even though its precise form and structure is unclear. The king THE DESTRUCTION OF THE GREAT ASSYRIAN CITIES WAS SO COMPLETE THAT, WITHIN TWO GENERATIONS OF THE EMPIRE’S FALL, NO ONE KNEW WHERE THE CITIES HAD BEEN. Erishum I built the temple of Ashur on the site in c. 1900/1905 BCE, and this has come to be the accepted date for the founding of an actual city on the site although, obviously, some form of city must have existed there prior to that date. The historian Wolfram von Soden writes, Because of a dearth of sources, very little is known of Assyria in the third millennium…Assyria did belong to the Empire of Akkad at times, as well as to the Third Dynasty of Ur.
Our main sources for this period are the many thousand Assyrian letters and documents from the trade colonies in Cappadocia, foremost of which was Kanesh (modern Kultepe) (49-50). The trade colony of Karum Kanesh (the Port of Kanesh) was among the most lucrative centres for trade in the ancient Near East and definitely the most important for the city of Ashur. Merchants from Ashur traveled to Kanesh, set up businesses, and then, after placing trusted employees (usually family members) in charge, returned to Ashur and supervised their business dealings from there. The historian Paul Kriwaczek notes:

Extracted from www.ancient.eu/Assyria/