The first known legally-political formation the Istrian ground was the kingdom of Histri after whom the peninsula was named, and which was in 178 BC conquered by the Romans. After the Romans, Istria came under the rule of the Goths in 476 AD, and after that the Byzantines (539) and the Franks (788). Under the Franks Istria was incorporated in different administrative formations, and about 1060 it became a margraviate. Its secular and religious rulers became the Patriarchs of Aquileia. Their rule lasted till the year 1420 when the Venetians subjugated most of the peninsula. The central part of Istria and its northeast remained under the rule of the Habsburgs from 1374 until the downfall of the Venetian Republic in 1797.
With the arrival of the French, great changes occured, as well in administrative as in the social aspect. From 1813 to 1918 Istria was a part of Austria.
After the First World War, Italy came into power. With the end of the Second World War Istria (except for the city of Muggia that remained in Italy) became Yugoslavian, that is, divided between Croatia and Slovenia. That partitioning was recently confirmed, after the breakdown of Yugoslavia, with the emergence of national countries of Croatia and Slovenia.
There are 348 773 inhabitants living in the area today.
Since the geographical position of Istria enabled the settlement of the peninsula during all past periods, it is difficult to precisely establish ethnic origin of the oldest inhabitants. According to tradition, there was mixing of the influences from the Italic and the Balkan peninsula, and from Panonia and the Central Europe.The first known inhabitants of the Istrian peninsula were the Histri.
The Histri lived in hill-forts (gradine, kašteliri,casteileri), settlements surrounded by defensive walls that were mostly built on natural elevations.The walls were built to conform to the surrounding terrain and many of them have been preserved until the present day. Later, new settlements were built on the basis of these hill-forts, so almost every present Istrian town on the hill is a continuance of Histrian hill-fort.
In 177 BC the Romans defeated the Histri at legendary Nesactium when the Histri comitted collective suicide. After that the Romans levelled to the ground Nesactium and fortresses of Mutila and Faveria.
The Romans first colonized only the coastal towns, while the hinterland still remained Histrian. Romanization of the Histri lasted for several centuries.
Already the first migration of the Slavs to Istria began with the encounter and permanent interaction of the two directions of migration. The first wave of Slav immigrants broke through to north Istra from the north, to present-day Brkini and Carst edge above Trieste (to the road Tergeste – Tarsatica) about the year 600 AD, while the other wave at approximately the same time came from the east to the area between Lipa and the foothills of Učka. The real spreading of the Slavs with the more permanent settling on Istrian peninsula occured at the end of the 8th century within the Franks’ colonization of waste and deserted land. Confirmation of this kind of settling can be found in charter of Rižana Council from 804 on which complaints of Istrian Roman indigenous inhabitants on the Slav settlers and Franks power-holders were discussed in front of the representatives of central Franks authorities. It is very likely that in that period, the Slavs inhabited eastern areas in the surroundings of Koper, Buzet and Pazin. Until the 14th century, Šavrinija (Koper/Capodistria region) and Ćićarija were colonized from the side of Notranjska, Buzet and northwestern karst side.
Until the middle of the 14th century, as a consequence of plague, malary, wars, and indigence caused by them, considerable demographic collapses ocurred, and it became very difficult for the population to survive on its own biological strength.
These unfavorable demographic conditions caused the need for an organized colonisation , so after several failed attempts of settling the southern Istria with inhabitants from Italy, the Venetians, primarily, but also the Austrians on their territory, began settling new population mostly from the area near the Turkish border. While in the southern Istria among the new inhabitants absolutely prevailed the ones from Dalmatia, in the upper part of peninsula we find considerable amount of settlers from the north. Among the newcomers, the Croatian and Slovene ethnic elements prevailed, and among the others, the only one to distinctively remain was the Istrio-Romanian (Žejane, Šušnjevica, Jasenovik, Brdo, Kostrčane), Montenegrin (Peroj) and till the end of the 19th century Albanian in several villages around Poreč. Already before organized colonisations, and while they lasted, and even later, spontaneous migrations or migrations by the will of a country system of governments and cities took place, like the migration of the population within the territory of the counts of Gorizia or the Patriarchs of Aquiliea.But beside all the misfortunes that hit Istria, it was still economically attractive enough for the settlers from different areas. In this way part of Slovenian tradesmen from Carniola permanantly settled in places in the surroundings of Koper/Capodistria, while the rest of the Slovenian population settled on the territory of the Pazin principality. Similar thing happened with the Friulian, Carniel and Venetian settlers that came on their own initiative or as villeins to landed estates.
Apart from the migrations from the areas out of Istria, also noticeable is another characteristic fluctuation of the Istrian population, and that is migration from one place to another within the peninsula.
We can by no means leave out two more instants of organized colonisation or at least colonisation encouraged by the authorities. The first happened in time of Italy with the favoring of migrations from the Apenine peninsula, with which they acquired Italian ethnic group. Situation completely reversed after the Second World War, and in northern Istria and the city of Pula in 1954 after the Free Territory of Trieste and Pula’s Anglo-American administration were disbanded, when that area was abandoned by huge percentage of population. If primarily they were Italians, there was among them, especially in the north, a considerable number of Croats and Slovenians who left either because of economic reasons, or because of the choice of a system of rule of law.Vacant settlements were colonized by newcomers from all parts of Yugoslavia who settled mostly in cities and thus completely changed the ethnic structure.