They gained control of Babylonia after the Hittite sack of the city in 1595 BC (i.e. 1531 BC per the short chronology), and established a dynasty based first in Babylon and later in Dur-Kurigalzu. The Kassites were members of a small military aristocracy but were efficient rulers and locally popular,and their 500-year reign laid an essential groundwork for the development of subsequent Babylonian culture. The chariot and the horse, which the Kassites worshipped, first came into use in Babylonia at this time.
The original homeland of the Kassites is not well established, but appears to have been located in the Zagros Mountains, in what is now the Lorestan Province of Iran. However, the Kassites were--like the Elamites, Gutians and Manneans who preceded them--linguistically unrelated to the Iranian-speaking peoples who came to dominate the region a millennium later. They first appeared in the annals of history in the 18th century BC when they attacked Babylonia in the 9th year of the reign of Samsu-iluna (reigned 1749-1712 BC), the son of Hammurabi. Samsu-iluna repelled them, as did Abi-Eshuh, but they subsequently gained control of Babylonia in 1570 BC, some 25 years after the fall of Babylon to the Hittites in 1595 BC, and went on to conquer the southern part of Mesopotamia, roughly corresponding to ancient Sumer and known as the Dynasty of the Sealand by 1520 BC. To the northeast control extended into the Diyala River region adjacent to the Zagros.
The Hittites had carried off the idol of the god Marduk, but the Kassite rulers regained possession, returned Marduk to Babylon, and made him the equal of the Kassite Shuqamuna. The circumstances of their rise to power are unknown, due to a lack of documentation from this so-called "Dark Age" period of widespread dislocation. No inscription or document in the Kassite language has been preserved, an absence that cannot be purely accidental, suggesting a severe regression of literacy in official circles. Babylon under Kassite rulers, who renamed the city Karanduniash, re-emerged as a political and military power in Mesopotamia. A newly built capital city Dur-Kurigalzu was named in honour of Kurigalzu I (early 14th century BC).
Their success was built upon the relative political stability that the Kassite monarchs achieved. They ruled Babylonia practically without interruption for almost four hundred years—the longest rule by any dynasty in Babylonian history.
Formation of Kassite power
The transformation of southern Mesopotamia into a territorial state, rather than a network of allied or combative city states, made Babylonia an international power, although it was often overshadowed by its northern neighbour, Assyria and by Elam to the east. Kassite kings established trade and diplomacy with Assyria. Puzur-Ashur III of Assyria and Burna-Buriash I signed a treaty agreeing the border between the two states in the mid-16th century BC, Egypt, Elam, and the Hittites, and the Kassite royal house intermarried with their royal families. There were foreign merchants in Babylon and other cities, and Babylonian merchants were active from Egypt (a major source of Nubian gold) to Assyria and Anatolia. Kassite weights and seals, the packet-identifying and measuring tools of commerce, have been found in as far afield as Thebes in Greece, in southern Armenia, and even in the Uluburun shipwreck off the southern coast of today's Turkey.
A further treaty between Kurigalzu I and Ashur-bel-nisheshu of Assyria was agreed in the mid-15th century BC. However, Babylonia found itself under attack and domination from Assyria for much of the next few centuries after the accession of Ashur-uballit I in 1365 BC who made Assyria (along with the Hittites and Egyptians) the major power in the Near East. Babylon was sacked by the Assyrian king Ashur-uballit I (1365-1330 BC) in the 1360s after the Kassite king in Babylon who was married to the daughter of Ashur-uballit was murdered. Ashur-uballit promptly marched into Babylonia and avenged his son-in-law, deposing the king and installing Kurigalzu II of the royal Kassite line as king there. His successor Enlil-nirari (1330-1319 BC) also attacked Babylonia and his great grandson Adad-nirari I (1307-1275 BC) annexed Babylonian territory when he became king. Tukulti-Ninurta I (1244-1208 BC) not content with merely dominating Babylonia went further, conquering Babylonia, deposing Kashtiliash IV and ruling there for eight years in person from 1235 BC to 1227 BC.
Control and prestige
The Kassite kings maintained control of their realm through a network of provinces administered by governors. Almost equal with the royal cities of Babylon
and Dur-Kurigalzu, the revived city of Nippur was the most important provincial center. Nippur, the formerly great city, which had been virtually abandoned c. 1730 BC, was rebuilt in the Kassite period, with temples meticulously re-built on their old foundations. In fact, under the Kassite government, the governor of Nippur, who took the Sumerian-derived title of Guennakku, ruled as a sort of secondary and lesser king. The prestige of Nippur was enough for a series of 13th-century BC Kassite kings to reassume the title 'governor of Nippur' for themselves.
Cylinder seal of Kassite king Kurigalzu II (c. 1332-1308 BC). Louvre Museum AOD 105
Other important centers during the Kassite period were Larsa, Sippar and Susa. After the Kassite dynasty was overthrown in 1155 BC, the system of provincial administration continued and the country remained united under the succeeding rule, the Second Dynasty of Isin.
Documentation of the Kassite period depends heavily on the scattered and disarticulated tablets from Nippur, where thousands of tablets and fragments have been excavated. They include administrative and legal texts, letters, seal inscriptions, kudurrus (land grants and administrative regulations), private votive inscriptions, and even a literary text (usually identified as a fragment of a historical epic). A number of seals have also been found. 
Kassite king Meli-Shipak II on a kudurru-Land presenting his daughter to the goddess ?unnubat-Nanaya. The eight-pointed star was Inanna-Ishtar's most common symbol. Here it is shown alongside the solar disk of her brother Shamash (Sumerian Utu) and the crescent moon of her father Sin (Sumerian Nanna) on a boundary stone of Meli-Shipak II, dating to the twelfth century BC.[i 1]
"Kassite rulers in Babylon were also scrupulous to follow existing forms of expression, and the public and private patterns of behavior "and even went beyond that--as zealous neophytes do, or outsiders, who take up a superior civilization--by favoring an extremely conservative attitude, at least in palace circles." (Oppenheim 1964, p. 62).
Fall of the Kassite kings
The Elamites conquered Babylonia in the 12th century BC, thus ending the Kassite state. The last Kassite king, Enlil-nadin-ahi, was taken to Susa and imprisoned there, where he also died.
The Kassites did briefly regain control over Babylonia with Dynasty V (1025-1004 BC); however, they were deposed once more, this time by an Aramean dynasty.
Kassites survived as a distinct ethnic group in the mountains of Lorestan (Luristan) long after the Kassite state collapsed. Babylonian records describe how the Assyrian king Sennacherib on his eastern campaign of 702 BC subdued the Kassites in a battle near Hulwan, Iran.
Kassite cylinder seal, ca. 16th-12th century BC.
Herodotus and other ancient Greek writers sometimes referred to the region around Susa as "Cissia", a variant of the Kassite name. However, it is not clear if Kassites were actually living in that region so late.
During the later Achaemenid period, the Kassites, referred to as "Kossaei", lived in the mountains to the east of Media and were one of several "predatory" mountain tribes that regularly extracted "gifts" from the Achaemenid Persians, according to a citation of Nearchus by Strabo (13.3.6).
As soldiers in foreign wars
But Kassites again fought on the Persian side in the Battle of Gaugamela in 331 BC, in which the Persian Empire fell to Alexander the Great, according to Diodorus Siculus (17.59) (who called them "Kossaei") and Curtius Rufus (4.12) (who called them "inhabitants of the Cossaean mountains"). According to Strabo's citation of Nearchus, Alexander later separately attacked the Kassites "in the winter", after which they stopped their tribute-seeking raids.
Strabo also wrote that the "Kossaei" contributed 13,000 archers to the army of Elymais in a war against Susa and Babylon. This statement is hard to understand, as Babylon had lost importance under Seleucid rule by the time Elymais emerged around 160 BC. If "Babylon" is understood to mean the Seleucids, then this battle would have occurred sometime between the emergence of Elymais and Strabo's death around 25 AD. If "Elymais" is understood to mean Elam, then the battle probably occurred in the 6th century BC. Susa was the capital of Elam and later of Elymais, so Strabo's statement implies that the Kassites intervened to support a particular group within Elam or Elymais against their own capital, which at that moment was apparently allied with or subject to Babylon or the Seleucids.
The latest evidence of Kassite culture is a reference by the 2nd-century geographer Ptolemy, who described "Kossaei" as living in the Susa region, adjacent to the "Elymeans". This could represent one of many cases where Ptolemy relied on out-of-date sources.
In spite of the fact that some of them took Babylonian names, the Kassites retained their traditional clan and tribal structure, in contrast to the smaller family unit of the Babylonians. They were proud of their affiliation with their tribal houses, rather than their own fathers, preserved their customs of fratriarchal property ownership and inheritance.
Herodotus was almost certainly referring to Kassites when he described "Ethiopians [from] above Egypt" in the Persian army that invaded Greece in 492 BC. Herodotus was presumably repeating an account that had used the name "Kush" (Cush), or something similar, to describe the Kassites; "Kush" was also, purely by coincidence, a name for Ethiopia. A similar confusion of Kassites with Ethiopians is evident in various ancient Greek accounts of the Trojan war hero Memnon, who was sometimes described as a "Kissian" and founder of Susa, and other times as Ethiopian. According to Herodotus, the "Asiatic Ethiopians" lived not in Kissia, but to the north, bordering on the "Paricanians" who in turn bordered on the Medes. The Kassites were not geographically linked to Kushites and Ethiopians, nor is there any documentation describing them as similar in appearance, and the Kassite language is regarded as a language isolate, utterly unrelated to any language of Ethiopia or Kush/Nubia, although more recently a possible relationship to the Hurro-Urartian family of Asia Minor has been proposed. However, the evidence for its genetic affiliation is meager due to the scarcity of extant texts.
According to the Encyclopædia Iranica:
There is not a single connected text in the Kassite language. The number of Kassite appellatives is restricted (slightly more than 60 vocables, mostly referring to colors, parts of the chariot, irrigation terms, plants, and titles). About 200 additional lexical elements can be gained by the analysis of the more numerous anthroponyms, toponyms, theonyms, and horse names used by the Kassites (see Balkan, 1954, passim; Jaritz, 1957 is to be used with caution). As is clear from this material, the Kassites spoke a language without a genetic relationship to any other known tongue.
The most notable Kassite artifacts are their Kudurrusteles. Used for marking boundaries and making proclamations, they were also carved with a high degree of artistic skill; they took a long time to make.
Male head from Dur-Kurigalzu, Iraq, Kassite, reign of Marduk-apla-iddina I. Iraq Museum
Door socket from Dur-Kurigalzu, Iraq. Kassite period, 14th century BCE. Sulaymaniyah Museum
Detail, facade of Inanna's Temple at Uruk, Kassite, 15th century BCE. Iraq Museum
Statue of a lion, Kassite, Iraq Museum
Limestone relief of a male figure from Tell al-Rimah, Iraq. Kassite. Iraq Museum
Terracotta plaque of a seated goddess, from Southern Mesopotamia, Iraq. Kassite period. Ancient Orient Museum
Duck-shaped weight mentioning the name of the priest Mashallim-Marduk, Kassite, from Babylon. Ancient Orient Museum
Lapis Lazuli fragment with building inscriptions, Kassite, from Iraq. Ancient Orient Museum
Kudurru mentioning the name of the Kassite king Kurigalzu II, from Nippur, Iraq, Ancient Orient Museum
Babylonian cuneiform tablet with a map from Nippur, Kassite period, 1550-1450 BCE
^Trevor Bryce, 2009, The Routledge Handbook of the Peoples and Places of Ancient Western Asia: The Near East from the Early Bronze Age to the Fall of the Persian Empire, Abingdon, Routledge, p. 375.
^Brinkman, J.A. 1976. Materials and Studies for Kassite Histo-r y. Vol. 1, pt. A, Catalogue of Cuneiform Sources Pertaining to Specific Monarchs of the Kassite Dynasty. Chicago: Chi-cago University Press.
^Brinkman, J.A. 2017. "Babylonia Under the Kassites: Some Aspects for Consideration." In Kardunia?: Babylonia Under the Kas-sites. Proceedings of the Symposium Held in Munich 30 Juni to 2 July 2011, 2 vols., edited by A. Bartelmus and K. Ster-nitzke, 1:1-44. UAVA 11.1. Berlin: De Gruyter.
^Schneider, Thomas (2003). "Kassitisch und Hurro-Urartäisch. Ein Diskussionsbeitrag zu möglichen lexikalischen Isoglossen". Altorientalische Forschungen (in German) (30): 372-381.
^ abcMyres, Sir John Lynton (1930). Who Were the Greeks?. University of California Press. p. 102. Among the names of Kassite kings are some which appear to contain Indo-European elements, as though they belonged to families which had once used Indo-European speech, but had lost it as their official language, through assimilation to the people of Kassite speech whose movements they were now directing. Some Kassite deities too seem to have Indo-European names.
^ abcPhillips, E. D. (1963). "The Peoples of the Highland: Vanished Cultures of Luristan, Mannai and Urartu". Vanished Civilizations of the Ancient World. McGraw-Hill: 241. Retrieved 2018. During the 2nd millennium the long process began by which Indo-European peoples from the northern steppes beyond the Caucasus established themselves about Western Asia, Iran and northern India. Their earliest pressure perhaps drove some the native peoples of the mountains to migrate or infiltrate and sometimes come as invaders into Mesopotamia and northern Syria, even in the 3rd millennium. The Indo-Europeans then drove their way through these peoples, drawing many of them in their train as subjects or allies, and appeared themselves early in the 2nd millennium as invaders and conquerors in the Near East. For the first half of the millennium the highlanders under Indo-European leadership dominated the older peoples of the plains, most of whom were Semites. The most powerful of these Indo-Europeans were the Hittites who ruled Anatolia, and later extended their dominion over northern Syria, but their connection with our three cultures is not direct, unles more Hittite influence was felt in Urartu than has so far appeared. Two other peoples are directly relevant, namely the Kassites from the Zagros mountains in the region of Luristan, and the Hurrians, who spread from regions further north, particularly from Armenia. Both were themselves native peoples of the highland, and spoke languages which were not Indo-European, but belonged to a group sometimes loosely called Caucasian, once widespread but later surviving only in the Caucasus. They were led by Indo- European aristocracies small in numbers but great in energy and achievement. They were the first to use the horse in war to draw the light chariot with spoked wheels. Indo-European names of gods at least appear among the Kassites, and of gods and rulers much more obviously among the Hurrians, in whom this element was clearly stronger. In both cases the names reveal the Indic branch of the Indo-European family, of which the main body moved through Iran to conquer northern India.
^Claudia Glatz, et. al., Babylonian Encounters in the Upper Diyala River Valley: Contextualizing the Results of Regional Survey and the 2016-2017 Excavations at Khani Masi, American Journal of Archaeology, Vol. 123, No. 3 (July 2019), pp. 439-471
^Donalds M Matthews, The Kassite Glyptic of Nippur, Freiburg, Switzerland / Göttingen,Germany: Universitätsverlag / Vandenhoeck Ruprecht, 1992
^J. Boardman et al. (eds) Cambridge Ancient History Vol III Pt 1 (2nd Ed) 1982