Since the dynastic marriage relations seem not to have brought an alliance between the two Illyrian States, in 168 BC Gentius allied with Perseus, the enemy of his father-in-law.

The following year Philip mass deportations from Paeonia where he filled the towns with Thracians and other barbarians, as being likely to remain more securely loyal to him in the coming hour of danger,[4] that is war with Rome.

In fact Philip's purpose for the Bastarnae was more specific to the security of Macedonia: They were to invade and eject the Dardanians under Monunius and take over their country, and later continue on their way through Illyria, finally reaching Italy.

Livy (XL, 574-9) writes that Philip's purpose was to wipe out the Dardanians and settle the Bastarnae in their lands (in the Polog valley), and send them to Italy and lay it waste, leaving their women and children in Dardania.

On the return of that embassy, Livy records that the Romans reported only that a Dardanian war was underway, and Appian adds that they had observed a major military build-up in Macedonia.

Perseus conquered a broad swath of territory in the south of the Dardanian State, also taking the region of Penesta (Polog valley) with its cities Uscana, Oene and Draudachus.

In order to stop the Dardanian raids into Macedonia, Perseus burned and destroyed the regions to the north and west of Mount Scardus (Sar Mountains), an area known thereafter as 'Deserted Illyria'.

Through these campaigns, Perseus annihilated the military bases that the Romans had built in the north-west of his kingdom, cut off for good the routes the Dardanians had used for their forays into Macedonia, and inserted himself like a wedge between Monunius and Gentius.

Since the dynastic marriage relations seem not to have brought an alliance between the two Illyrian States, in 168 BC Gentius allied with Perseus, the enemy of his father-in-law.

After the destruction of Macedonia in 167 BC, the Dardanians ask the consul Paullus Aemilius for control of Paeonia, but he refused, giving them only the right to trade in salt there.