Please explain why is there no “to” before “guide” in this sentence

It's an old-fashioned, sort of poetic way of speaking.  Civ is filled with that type of stuff, I can't explain the grammar behind it but you probably won't run into anyone speaking like this in real life

English can get away with dropping "to" sometimes, specifically with "only." We need only show them. He need only read it. It's an archaic construction, but entirely understandable.

This is not an archaic sentence structure. When you have "modal verb + other verb" you don't need the "to" as part of the infinitive. For example: I can help them. \ You could listen! \ You mustn't grumble. \ You might be. \ In your example "need" has become a modal verb. Need isn't usually a modal verb but the reordering of the adverb only makes it one. You're right the more common structure would be: We only need to guide them.

This is an example of a "bare infinitive", where the "to" is dropped after a modal verb. In everyday english, "need" is not often treated as a modal verb, but it technically is, therefore the "to" can be dropped. If you do this in casual english after "need" you may sound pretentious. [https://www.grammar-monster.com/glossary/bare-infinitive.htm](https://www.grammar-monster.com/glossary/bare-infinitive.htm)

Iirc this is an archaic sentence structure that is still used now and then

“Need only” + bare infinitive is a sort of set phrase. There isn’t a generalizable grammatical logic behind this.

Say it in a European accent and you'll get it.

I’d say it’s archaic to drop the “to”. You could also say either “we need only to guide them” or “we need to only guide them”. Or even “we only need to guide them”. Depending on where you felt the minor emphasis difference was.

It's a kinda archaic way of speaking. This sort of language gets used in medieval and medieval fantasy fiction a lot.

I believe it’s called the “bare infinitive.” You can leave out the “to” if doing so wouldn’t change the meaning of the sentence or make it ambiguous. To most English speakers, this form sounds old-timey, so it’s most often used in formal speech or in fiction based on historical periods. It is entirely a stylistic choice, so you wouldn’t be incorrect for saying “we need only to guide them.” A more common form would be “we only need to guide them.”

If you watch or read Lord of the Rings I feel like this is how Aragorn tends to speak.

Not so sure “only need” has the same meaning as “need only. “ think of the insurance advertisement that incorrectly says “Only pay for what you need” when correct English or meaning would be “Pay only for what you need. “

What game is this ?

"Need" is technically a modal verb, like "must" or "can", though most people don't use it as one anymore.

As other replies have mentioned, need is a semi-modal verb. It is sometimes used as a modal verb, almost always in conjunction with a negative word such as not, no, hardly, scarcely or only. I need scarcely mention that this is uncommon in conversational American English. One need only read the replies here to realize that. In British English, this structure is more common and they often abbreviate "need not" to "needn't".

I'm a big civ player and I think it's be a great resource, but all of the quotes when you build wonders or discover techs and civics will all be in either in very old fashioned English or translated from another language so take note of that. IDK if you're new to the game but check out the ? in the top right

it's the subjunctive case. Used all the time in Spanish, not as often in English. [https://englishgrammarclub.com/subjunctive/](https://englishgrammarclub.com/subjunctive/)

The other comments are correct, but maybe not very intuitive. If you replace "need" with "shall" or "will", the sentence sounds fine. Using the verb "need" like that (modal verb) is not common outside of old-timey idioms: "Need I say more?" (need as modal verb) "Must you always doubt me?" (must as modal verb)

It’s not wrong, but it’s not how a native speaker would say it.

It’s an old fashioned way of saying it, they have used it to be suitable for this (seemingly traditional) game

“need” + bare verb construction It can only be used in negative sentences. The “only” in this case makes the sentence negative, and allows this use of “need”. Note that “we need guide them” (positive sentence without “only”) is incorrect.

"Need" used to work the same as other verbs such as "might", "may", "can" or "should".

It's not only sounding old fashioned. It's also sounding slightly mystical in a very clichéd way, and possibly also a little condescending. Think 'bad 1970s drama with mildly racist stereotypes' and that captures the connotations for me. You would never use a construction like this in everyday speech now.

Do not think the convetion of "need only" is equal to "need." The transitivity of the two phrases are not the same. That's all.

Because it’s a game aka product of a private, commercial entity. Also, some people don’t care about using current and formally accepted English prose.