In the Middle Bronze Age Assyria was a region on the Upper Tigris river, named for its original capital, the ancient city of Assur (Akkadian: Aššur; Hebrew: אַשּׁוּר Aššûr, Aramaic: Aṯûr). Later, as a nation and empire that came to control all of the Fertile Crescent, Egypt and much of Anatolia, the term "Assyria proper" referred to roughly the northern half of Mesopotamia (the southern half being Babylonia), with Nineveh as its capital.
The Assyrian kings controlled a large kingdom at three different times in history. These are called the Old (20th to 15th c. BC), Middle (15th to 10th c. BC), and Neo-Assyrian (911-612 B.C.) kingdoms, or periods, of which the last is the most well known and best documented.
The Assyrian homeland was located near a mountainous region, extending along the Tigris as far as the high Gordiaean or Carduchian mountain range of Armenia, sometimes known as the "Mountains of Ashur".
Assyrians invented excavation to undermine city walls, battering rams to knock down walls and gates, concept of a corps of engineers, who bridged rivers with pontoons or provided soldiers with inflatable skins for swimming.

Old Assyrian city-states and kingdoms
The city-state of Ashur had extensive contact with cities on the Anatolian plateau. The Assyrians established "merchant colonies" in Cappadocia, e.g., at Kanesh (modern Kültepe) circa 1920 BC–1840 BC and 1798 BC–1740 BC. These colonies, called karum, the Akkadian word for 'port', were attached to Anatolian cities, but physically separate, and had special tax status. They must have arisen from a long tradition of trade between Ashur and the Anatolian cities, but no archaeological or written records show this. The trade consisted of metal (perhaps lead or tin; the terminology here is not entirely clear) and textiles from Assyria, that were traded for precious metals in Anatolia.

City state of Ashur
The city of Ashur was conquered by Shamshi-Adad I (1813 BC–1791 BC) in the expansion of Amorite tribes from the Khabur river delta. He put his son Ishme-Dagan on the throne of nearby city Ekallatum, and allowed the former Anatolian trade to continue. Shamshi-Adad I also conquered the kingdom of Mari on the Euphrates and put another of his sons, Yasmah-Adad on the throne there. Shamshi-Adad's kingdom now encompassed the whole of northern Mesopotamia. He himself resided in a new capital city founded in the Khabur valley, called Shubat-Enlil. Ishme-Dagan inherited the kingdom, but Yasmah-Adad was overthrown and Mari was lost. The new king of Mari allied himself with Hammurabi of Babylon. Assyria now faced the rising power of Babylon in the south. Ishme-Dagan responded by making an alliance with the enemies of Babylon, and the power struggle continued for decades.

Kingdom of Shamshi-Adad I
Hammurabi eventually prevailed over Ishme-Dagan, and conquered Ashur for Babylon. With Hammurabi, the various karum in Anatolia ceased trade activity — probably because the goods of Assyria were now being traded with the Babylonians' partners.
Assyria was ruled by vassal kings dependent on the Babylonians for a century. After Babylon fell to the Kassites, the Hurrians dominated the northern region, including Assur.

Assyria reduced to vassal states
(Scholars variously date the beginning of the "Middle Assyrian period" to either the fall of the Old Assyrian kingdom of Shamshi-Adad I, or to the ascension of Ashur-uballit I to the throne of Assyria.)

Middle Assyrian period
In the 15th century BC, Saushtatar, king of Hanilgalbat (Hurrians of Mitanni), sacked Ashur and made Assyria a vassal. Assyria paid tribute to Hanilgalbat until Mitanni power collapsed from Hittite pressure from the north-west and Assyrian pressure from the east, enabling Ashur-uballit I (1365 BC–1330 BC) to again make Assyria an independent and conquering power at the expense of Babylonia; and a time came when the Kassite king in Babylon was glad to marry the daughter of Ashur-uballit, whose letters to Akhenaten of Egypt form part of the Amarna letters. This marriage led to disastrous results, as the Kassite faction at court murdered the Babylonian king and placed a pretender on the throne. Assur-uballit promptly marched into Babylonia and avenged his son-in-law, making Kurigalzu of the royal line king there.

Ashur-uballit I
Hanilgalbat was finally conquered under Adad-nirari I, who described himself as a "Great-King" (Sharru rabû) in letters to the Hittite rulers. The successor of Adad-nirari I, Shalmaneser I (c. 1300 BC), threw off the pretense of Babylonian suzerainty, made Calah his capital, and continued expansion to the northwest, mainly at the expense of the Hittites, reaching Carchemish and beyond.
Shalmaneser's son and successor, Tukulti-Ninurta I, deposed Kadashman-Buriash of Babylon and ruled there himself as king for seven years, taking on the old title "King of Sumer and Akkad". Another weak period for Assyria followed when Babylon revolted against Tukulti-Ninurta, and later even made Assyria tributary during the reigns of the Babylonian kings Melishipak II and Marduk-apal-iddin I.

Assyrian expansion
As the Hittite empire collapsed from onslaught of the Phrygians (called Mushki in Assyrian annals), Babylon and Assyria began to vie for Amorite regions, formerly under firm Hittite control. The Assyrian king Ashur-resh-ishi I defeated Nebuchadnezzar I of Babylon in a battle, when their forces encountered one another in this region.
The son of Ashur-resh-ishi's, Tiglath-Pileser I, may be regarded as the founder of the first Assyrian empire. In 1120 BC, he crossed the Euphrates, capturing Carchemish, and defeated the Mushki and the remnants of the Hittites—even claiming to reach the Black Sea. He advanced to the Mediterranean, subjugating Phoenicia, where he hunted wild bulls. He also marched into Babylon twice, assuming the old title "King of Sumer and Akkad", although he was unable to depose the actual king in Babylonia, where the old Kassite dynasty had now succumbed to an Elamite one.

Tiglath-Pileser I reaches the Mediterranean Sea
Assyria had difficulties with keeping the trade routes open. Unlike the situation in the Old Assyrian period, the Anatolian metal trade was effectively dominated by the Hittites and the Hurrians. They also controlled the Mediterranean ports while the Kassites controlled the river route south to the Persian Gulf.
The Middle Assyrian kingdom was well organized and in the firm control of the king who also functioned as the High Priest of Ashur, the state god. He had certain obligations to fulfill in the cult and had to provide resources for the temples. The priesthood became a major power in Assyrian society. Conflicts with the priesthood are thought to have been behind the murder of king Tukulti-Ninurta I.
The main Assyrian cities of the middle period were Ashur, Kalhu and Nineveh, all situated in the Tigris River valley. At the end of the Bronze Age, Nineveh was considerably smaller than Babylon, but still one of the world's major cities (population ca. 33,000). By the end of the Neo-Assyrian period, it had grown to a population of some 120,000, and was possibly the largest city of that time.
All free male citizens were obliged to serve in the army for a time, a system which was called the ilku-service. The Assyrian law code, which was notable for its repressive attitude towards women in their society, was compiled during this period.

Society in the Middle Assyrian period

Main article: Neo-Assyrian Empire Neo-Assyrian Empire
The ancient people of Assyria spoke an Assyrian dialect of the Akkadian language, a branch of the Semitic languages. The first inscriptions, called Old Assyrian (OA), were made in the Old Assyrian period. In the Neo-Assyrian period the Aramaic language became increasingly common, more so than Akkadian - this was thought to be largely due to the mass deportations undertaken by Assyrian kings, in which large Aramaic-speaking populations, conquered by the Assyrians, were relocated to other parts of the empire. The ancient Assyrians also used the Sumerian language in their literature and liturgy, although to a more limited extent in the Middle- and Neo-Assyrian periods, when Akkadian became the main literary language.
The utter and complete destruction of the Assyrian capitals of Nineveh and Assur by Babylonians and Medians ensured that the bilingual elite, perhaps the few remaining still competent in Akkadian, were wiped out. By the 6th century B.C., much of the Assyrian population that survived used Aramaic and not the cuneiform Akkadian. In time, Akkadian would no longer be used by the Assyrians, although many aspects of the culture associated, such as naming with Assur, continued, and do so today.

Language

Main article: Art and architecture of Babylonia and Assyria Legacy and rediscovery