Es würde sehr helfen, wenn Du uns sagtest, was Du auf deutsch ausdrücken möchtest.

... so their fervour was artificially prodded by ...

leave the 'on', I'd say.

Prod or prod on fervor (or fervour) sounds strange to me. You might want to try verbs like incite or encourage, depending on the level of intensity involved.

BTW, I would say futility, not futileness.

A final thought: It would be helpful if you provided your German version. Having to guess what you mean is a waste of time and can easily result in misunderstanding.

I actually like the "prod on" variant here.

It indicates that even their fervour was somewhat lacking.

The image created here is that of a donkey herder that keeps poking the animal in order to keep it moving.

In the same way here people are not trying to stir up trouble - their keep prodding and poking in order to incite people, but even though people may be rioting their heart is not in it.

Because the OP's suggestion sounded so odd to me (a native speaker of English), I checked the British National Corpus and the Corpus of Contemporary American English before writing #3, but I couldn't find any examples of prod/prod on fervor/fervor.

In the meantime I have another suggestion. Assuming that the OP means something like aufheizen, whip up would be a possibility.

'To prod on' or here "...prodded on..." does seem a bit out of context.

I think "...their fervour was brought on artifically by..." might fit a bit better.

It would make more sense to you if you re-wrote the sentence in an active voice. "..., so external agitators prodded (on) their fervour..."

Then, in an active voice, "persuade" might be the best choice.

But "whip up" sounds so dynamic.

"prod on their fervour" reminds me of "nasses Papier in Brand stecken"

But "whip up" sounds so dynamic.
1. I don't know what you mean by so dynamic. How dynamic is that in your view?
2. Unlike you apparently, I don't know how "dynyamic" the OP wants his/her verb to be.
3. "Whip up" would at least be idiomatic.

@0: by exterior agitators - I don't think "exterior" is the correct word here. Do you mean agitators who are not members of the local population? If you do, and I assume you do, outside agitators is the established term.

Thank you, I will use 'whip up"!
And "futility"!

Or external agitators -- just not exterior, which is typically used for the outside of buildings or other structures.

I also agree that 'prod,' with or without 'on,' isn't very idiomatic. Better options might include 'spurred on' or 'goaded,' if you use people as the subject. But if you use 'fervor' as the subject, you need a different verb.

Local residents were spurred on / goaded into action by external agitators.
Their fervor was stirred up / heightened by outside agitators.

Also, 'so' here is not a true causal connector; there's no direct logical relation between the two unsupported statements of opinion. Perhaps you mean something like 'For that reason it seems likely that they were stirred up by outsiders.'

(Actually, if this is for an academic essay or for journalism, you would need to give evidence for both assertions -- that local residents were incapable of, or uninterested in, protesting on their own behalf, and that outside agitators were in fact present. I must say I'm skeptical on the face of it, as those kinds of claims are typical of authoritarian governments.)