Mesopotamia (/ˌmɛsəpəˈteɪmiə/, from the Ancient Greek: Μεσοποταμία “[land] between rivers”; Arabic: بلاد الرافدين (bilād al-rāfidayn); Syriac: ܒܝܬ ܢܗܪܝܢ (Beth Nahrain) “land of rivers”) is a name for the area of the Tigris–Euphrates river system, corresponding to modern-day Iraq, Kuwait, the northeastern section of Syria and to a much lesser extent southeastern Turkey and smaller parts of southwestern Iran.
Widely considered to be the cradle of civilization in the West, Bronze Age Mesopotamia included Sumer and the Akkadian, Babylonian, and Assyrian empires, all native to the territory of modern-day Iraq. In the Iron Age, it was controlled by the Neo-Assyrian and Neo-Babylonian empires. The indigenous Sumerians and Akkadians (including Assyrians and Babylonians) dominated Mesopotamia from the beginning of written history (c. 3100 BC) to the fall of Babylon in 539 BC, when it was conquered by the Achaemenid Empire. It fell to Alexander the Great in 332 BC, and after his death, it became part of the Greek Seleucid Empire.
Around 150 BC, Mesopotamia was under the control of the Parthians. Mesopotamia became a battleground between the Romans and Parthians, with parts of Mesopotamia coming under ephemeral Roman control. In AD 226, it fell to the Sassanid Persians and remained under Persian rule until the 7th-century Arab Islamic conquest of the Sassanid Empire. A number of primarily neo Assyrian and Christian native Mesopotamian states existed between the 1st century BC and 3rd century AD, including Adiabene, Osroene, and Hatra. Mesopotamia encompasses the land between the Euphrates and Tigris rivers, both of which have their headwaters in the mountains of Armenia in modern-day Turkey. Both rivers are fed by numerous tributaries, and the entire river system drains a vast mountainous region. Overland routes in Mesopotamia usually follow the Euphrates because the banks of the Tigris are frequently steep and difficult. The climate of the region is semi-arid with a vast desert expanse in the north which gives way to a 15,000 square kilometres (5,800 sq mi) region of marshes, lagoons, mud flats, and reed banks in the south. In the extreme south, the Euphrates and the Tigris unite and empty into the Persian Gulf.
The arid environment which ranges from the northern areas of rain-fed agriculture to the south where irrigation of agriculture is essential if a surplus energy returned on energy invested (EROEI) is to be obtained. This irrigation is aided by a high water table and by melting snows from the high peaks of the Zagros Mountains and from the Armenian cordillera, the source of the Tigris and Euphrates Rivers that give the region its name. The usefulness of irrigation depends upon the ability to mobilize sufficient labor for the construction and maintenance of canals, and this, from the earliest period, has assisted the development of urban settlements and centralized systems of political authority.
Agriculture throughout the region has been supplemented by nomadic pastoralism, where tent-dwelling nomads herded sheep and goats (and later camels) from the river pastures in the dry summer months, out into seasonal grazing lands on the desert fringe in the wet winter season. The area is generally lacking in building stone, precious metals and timber, and so historically has relied upon long-distance trade of agricultural products to secure these items from outlying areas. In the marshlands to the south of the area, a complex water-borne fishing culture has existed since prehistoric times, and has added to the cultural mix.
Periodic breakdowns in the cultural system have occurred for a number of reasons. The demands for labor has from time to time led to population increases that push the limits of the ecological carrying capacity, and should a period of climatic instability ensue, collapsing central government and declining populations can occur. Alternatively, military vulnerability to invasion from marginal hill tribes or nomadic pastoralists has led to periods of trade collapse and neglect of irrigation systems. Equally, centripetal tendencies amongst city states has meant that central authority over the whole region, when imposed, has tended to be ephemeral, and localism has fragmented power into tribal or smaller regional units. These trends have continued to the present day in Iraq.