A Deeper Cause
It is too easy to explain the Batavian revolt from the two motives that we discussed in the preceding part of this article: the forced recruitment and the presence of a prince with a grudge. There has to be a deeper cause; after all, if the Batavians were content with Roman rule, they would have accepted the forced recruitment as an unpleasant but temporary measure, and would not have followed Julius Civilis. We must admit that we do not know what this deeper cause, but we can make some educated guesses, and make a list of contributing factors.
In the first place, Julius Civilis had at least two powerful personal motives. Tacitus mentions the -perhaps unlawful- execution of Civilis' brother Paulus, which must have been sufficient for anybody to start looking for revenge. An additional motive may have been the restoration of royal power. As we have already seen (above) that Julius Civilis belonged to the leading Batavian family, and that his ancestors had been kings. It is impossible that the thought about restoration did not cross Civilis' mind. This motive, however, is not mentioned by Tacitus.
He does, however, quote from a speech by the Batavian leader, in which he presented the corrupt recruitment practices as proof for the fact that the Romans did not consider the Batavians to be allies, but subjects ('the alliance is no longer observed on the old terms: we are treated as chattels'). Unfortunately, we can not establish whether Civilis really said something like this, and we have a right to be doubtful. After all, how can Tacitus possibly have known what Civilis had said? Besides, the corruption of decadent Roman magistrates is one of the leading themes of Tacitus. We may reasonably assume that the speech of Civilis, in which he focuses on the rupture of the alliance, is an invention. It is too legalistic.
Nonetheless, the levy was a heavy burden. We already noticed that every Batavian family had at least one son in the army, and that Vitellius was demanding too much. There is no reason to deny that this was one of the factors that contributed to the outbreak of the war.

Taxes
Sometimes, Tacitus makes the Batavian leader say that he is defending the freedom of his compatriots. Unfortunately, in ancient literature, barbarians always are thirsting for freedom. The motive is highly suspect. An additional complication is that we do not know what is meant with 'freedom'. Were the Batavians looking for real independence and autonomy? Or was Julius Civilis trying to give more power to the Batavian elite?
There is some evidence that may corroborate the last hypothesis. The old aristocracy of the tribes now living in the Roman empire, had received the prestigious Roman citizenship several generations ago. Those who had been patronized by Julius Caesar and the emperor Augustus, had as family name Julius, plus an additional personal surname (e.g., Julius Civilis). But a new generation was becoming influential. They had received the citizenship from Tiberius, Claudius, or Nero, and had Claudius as their new family names (e.g., Claudius Labeo). There may have been some tension between the first and second generation, because the 'old Romans' were probably not happy to share their power with the newcomers; as we will see below, one of Julius Civilis' personal enemies was a Claudius. It is possible that Civilis wanted to restore the rights of the old aristocracy.
There may have been a religious motive, because we know that a Bructerian prophetess called Veleda predicted the victory of the Batavians. Later, she was awarded with the Roman commander Munius Lupercus (as slave) and the flagship of the Roman navy. However, it is not known whether she incited the rebels or merely predicted victory.
It may also be noted that the Batavian revolt does not belong to the 'normal' rebellions of the first century, like that of Julius Florus and Julius Sacrovir in Gaul in 21, that of queen Boudicca in Britain in 60, and that of the Jews in 66: these were caused by oppressive taxes. The Batavian revolt was not caused by financial troubles. It is rather logic to me, as I don't give a damn about money, that I regard the Batavians as my ancestors.
So we are left with several -sometimes conflicting- factors that may have played a role. Julius Civilis wanted to avenge his brother and may have wanted to become king; the old tribal elite may have wanted to regain its former power; and perhaps the tribe as a whole dreamed of an independent state - something that the Frisians and Chauci, two tribes in the north, had obtained in 28. What bound them together, was bitter resentment because of the oppressive recruitment.