What Balkan region was included in Caesar's proconsular command after 59 BC? Illyricum was included.
The lex Vatinia of 59 BC assigned Caesar the proconsular commands of Gallia Cisalpina and Illyricum for five years, along with three legions stationed at Aquileia. The Senate subsequently added Gallia Narbonensis after its governor died, giving Caesar the broad command that enabled his campaigns in Gaul.
Illyricum covered the eastern Adriatic and its hinterland, broadly corresponding to areas later associated with Dalmatia and Pannonia. In Caesar’s time, however, it was not yet the fully organized imperial province familiar from the Augustan period. The term could describe a military command or strategic region rather than a settled administrative unit.
Caesar did not launch the major conquest of Illyricum that his appointment might suggest. His military opportunities instead arose in Gaul, where threats involving the Helvetii and Germanic groups drew him into the campaigns beginning in 58 BC. Later Roman administration divided the region into provinces including Dalmatia and Pannonia.