Short answers, pulled from the story.
The Roman province of Dalmatia covered the northern part of present-day Albania, much of Croatia, Bosnia and Herzegovina, Montenegro, and Serbia. It encompassed a substantially larger area than the modern Croatian and Montenegrin region known as Dalmatia.
Dalmatia takes its name from the Dalmatae, an Illyrian tribe that inhabited the central section of the eastern Adriatic coast. Before the name Dalmatia was adopted, the Romans called the wider region Illyricum, derived from the Greek name Illyria.
The exact date of the split is disputed. A military diploma dated July 61 AD references auxiliary units from the Pannonian part of Illyricum, and one scholar, Sasel-Kos, concludes the formal division occurred during the reign of Vespasian, who ruled from 69 to 79 AD.
The Batonian War, known in Latin as the Bellum Batonianum, was a large-scale rebellion in the province of Illyricum between 6 and 9 AD. It is among the earliest events in which Dalmatia appears as a distinct military command, with Gaius Vibius Postumus serving as commander under Germanicus in 9 AD.
Julius Nepos governed Dalmatia starting in 468 after the death of the rebel commander Marcellinus. Leo I elevated him to western emperor in 474, but he was deposed in 475 and returned to Dalmatia, where he continued to govern until his assassination in 480.
In 488, the eastern emperor Zeno sent Theodoric the Great, king of the Ostrogoths, to Italy to defeat Odoacer. After a four-year war Theodoric killed Odoacer and established the Ostrogothic Kingdom, bringing Dalmatia and the rest of the former diocese of Pannonia under Ostrogothic rule.