Queen Teuta had submitted to Rome in 228 BCE, but the Illyrian kingdom of the interior had not been destroyed, and the Romans in 219 BCE send a second naval expedition against Illyria, in which their forces overrun the Illyrian settlements in the Neretva River valley and …

…one noble, Sandalj Hranić, also engages in tactical alliances against the Bosnian rulers, establishing his own rule over the territory of Hum, only nominally recognizing Bosnian overlordship.

Hercegovina (also spelled Herzegovina), centered on the city of Mostar, is established as a duchy separate from Bosnia in 1448, when, in a document sent to Holy Roman Emperor Frederick III on January 20, 1448, Stephen Vukčić Kosača styles himself "Duke of Saint Sava (Vojvoda Svetog Save), lord of Hum and Primorje (Gospodar Humski i Primorski), Grand Duke (Herzog), and forces Bosnia to recognize him as such.

Hercegovina’s name derives from the German Herzog ("duke"), the title borne by its rulers.

Herzegovina’s unofficial capital of Mostar had been first mentioned in 1452.

Only a few years later, it is invaded by the Ottomans.

The Ottomans are the first to begin officially using the name Herzegovina for the region, when the beg of Bosnia Isa-beg Ishaković mentions the name in a letter from 1454.

Most of Hercegovina, heretofore a client state of Hungary-Croatia, falls to the Ottoman Turks shortly after the death of Duke Stjepan Vukcic in 1466.

Many of the Bogomils of Hercegovina and …

...Herzegovina from their capitals at Travnik and Mostar, but few Turks actually settle in this territory.

Economic life declines and the regions grow isolated from Europe and even Constantinople.

As the sultan's military expenses grow, large estates replace small farms, and peasant taxes are raised substantially.

A third church in Herzegovina, the Serbian Orthodox, has also competed for Christian adherents.

Christianity is thus structurally weaker in Bosnia than in almost any other part of the Balkans.

The motives that incline Bosnians to adopt Islam are economic: the prosperous cities of Sarajevo and Mostar are mainly Muslim, and it is not possible to lead a full civic life there without converting to Islam.

Other motives include the privileged legal status enjoyed by Muslims and, possibly, a desire to avoid the harac, though Muslims are subject, unlike Christians, both to the alms tax and to the duties of general military service. (Modern historians have largely disproven the traditional belief that Bosnian noblemen converted en masse to Islam in order to keep their estates).

Another way in which Bosnia differs from other parts of the Ottoman Balkans is that for most of last century Bosnia has been a frontier province, facing two of the empire's most important enemies, Austria-Hungary and Venice.

To fill up depopulated areas of northern and western Bosnia, the Ottomans have encouraged the migration of large numbers of hardy settlers with military skills from Serbia and Herzegovina.

Many of these settlers are Vlachs, members of a pre-Slav Balkan population that has acquired a Latinate language and specialized in stockbreeding, horse raising, long-distance trade, and fighting.

Most are members of the Serbian Orthodox church.

Before the Ottoman conquest, that church had had very few members in the Bosnian lands outside Herzegovina and the eastern strip of the Drina valley; there is no definite evidence of any Orthodox church buildings in central, northern, or western Bosnia before 1463.

Several Orthodox monasteries have been built during the sixteenth century, however, in those parts of Bosnia, apparently to serve the newly settled Orthodox population there.

...Mostar, where such urban culture flourishes, enjoy a large degree of autonomy under elected officials.