Were they coerced, or were they simply tricked?

They were tricked through coercive means.

No, they were not acting in the good faith. Intentions were malafide.

That makes the 'victim' a dupe.

Do you mean to say that even if some people were able to see through the ruse, they'd still be coerced into changing religion?

No, I don't mean that. People were totally oblivious.

Weather Vane's suggestion is good then.

@user405662 Well, that's the best suggestion so far.

Very closely related (*at least): more concise word or phrase for people who have been taken advantage of. Plenty of answers, including 'dupe', but lacking the 'because they lacked the intellectual wherewithal to evaluate it beforehand' condition.

Is there one word for being deceived into complying with ... is also *very closely related.

In French law, such persons are the "victimes d'un abus de faiblesse" (victims of abuse of weakness), but in English/US law, they are victims of undue influence ("unduly influenced persons"), but this term is not as specific as the French one.

The simple answer is that this isn't coercion. Coercion entails knowing the implications of what you are doing. When they don't know or are misled, they are being scammed.

I'll provide a few words for consideration: converted, influenced and compelled.

"They were tricked through coercive means." That's not coercion. Coercion entails the victim is aware of what it is they're made to do, but they are still "choosing" to do so, for ulterior reasons. The coercive nature implies that the coercer is choosing to enact those undesirable ulterior outcomes if the victim does not comply. For example, robbery is coercion, you are forced to "choose" to hand over your valuables and not fight back, under threat of being hurt/killed. None of this is trickery, the victim is aware that they are being made to do something they don't want to.

Given the clarification that the people in question were more "tricked" than "coerced", this may be relevant.

If someone is coercing your thoughts or actions, you might be a thrall - vocabulary.com/dictionary/thrall

Contra the poster and their description, I suspect that there may actually have been coercion in some cases. E.g. convert (and submit informally to our authority) or we will conquer you and make you a formal colony; if you do not convert, then you will not be able to be a full part of the colonial society; and so forth.

@Obie2.0 the context seems to be about religious conversion.

@WeatherVane - And?

@Obie2.0 you seem to have digressed to colonisation. Perhaps you can ask the OP to add more context.

@WeatherVane - They are talking about conversion from traditional religions to organized religions (I guess they mean Christianity and maybe Islam) in Africa and Asia. While that does still happen, it was much more common during the various countries' colonial periods, so I believe that is most likely what the question is talking about.

@Obie2.0 perhaps you can ask the OP to add more context.

Let us continue this discussion in chat.

@Flater I understand now.

@Obie2.0 You are absolutely right. I was talking about the colonial times. After having understood the hues of these words - trickery, coercion, I think it was trickery and coercion both which were both applied during colonial times in different proportion.