What sparked the War of Spartacus?
Lentulus Vatia was the owner of the gladiator school which brought Spartacus. At the school would have been men from different parts of the empire. In Barry Strauss' “The Spartacus War” it is suggested that Lentulus purchased men without a thought of their origins. In doing so, he unwittingly grouped together men that, while seemingly different, were united in their hatred of Rome and their support of Mithridates, who was waging a war in the east.
The sources say that Lentulus' school contained Gauls. While there were almost certainly Gauls, some of Lentulus' Celts may have come from the Balkans where Rome had been fighting for the previous two decades. A particular tribe known as the Scordisci, were neighbours of the Thracians. If Lentulus had purchased some Scordisci, he had brought the wrong type of Celt. The potntial for solidarity in the group was high.
Spartacus had been a soldier, and possibly Thracian royalty, who fought on the side of Rome. For some unknown reason he ended up in slavery. Strauss makes the suggestion that Spartacus defected to Mithradates. If he had been of Thracian nobility, there is a strong chance that he was capable of leading an army.
Spartacus' lover, a Thracian woman whose name is unknown. We do know that she was a Bacchante, a worshipper of Dionysus. The cult of Dionysus had been banned in Rome and was frowned upon by the nobility. However, outside of Rome, and among the poor and the slaves of Italy, the cult flourished. The cult gave the lower classes hope and a fighting spirit that Rome feared. Followers of Dionysus had played a part in two previous slave uprisings in Sicily.
Spartacus' lover had a prophetic dream that implied that the gladiator would be surrounded by powerful enemies and that he would overcome them. It is not known whether this was before of after the uprising, but either way it was great propaganda.
So, due to Lentulus Vatia's ignorance in the origin of his gladiators, he trained and armed a small army with its own experienced leader who owned his own PR machine.