Learn Hardcore Croatian: Pročitavši članak o politici, mladi građanin je manje sumnjao u budućnost države. - Having read an article about politics, the young citizen doubted the future of the country less.

It is made from the perfective verb pročitati (to read through, to finish reading).
For many perfective verbs ending in -ti, you form this by taking the infinitive stem and adding -vši:
- pročitati → pročitavši
- napisati → napisavši
It expresses an action that happened before the action of the main verb, and is done by the same subject as in the main clause.

So the structure Pročitavši članak o politici, ... means roughly Having read the article about politics, ...

Who is the subject of Pročitavši if there is no noun or pronoun attached?

The subject of Pročitavši is always understood to be the same as the subject of the main clause.

In this sentence, the main clause subject is mladi građanin (the young citizen). So we understand:

Pročitavši članak o politici, mladi građanin...
≈ After he (the young citizen) read the article about politics, the young citizen...

You cannot use this construction if the “doer” of Pročitavši and the subject of the main clause are different; that would be considered incorrect or at least very bad style in Croatian.

Can I replace Pročitavši članak o politici with a clause like in English?

Yes. You can express the same idea with a finite clause. Some common equivalents:

Kad je pročitao članak o politici, mladi građanin je manje sumnjao u budućnost države.
(When he read the article about politics, the young citizen doubted the future of the state less.)
Nakon što je pročitao članak o politici, mladi građanin je manje sumnjao u budućnost države.
(After he read the article about politics, ...)

The version with Pročitavši is:

a bit more compact
somewhat more formal / literary in tone

Using kad or nakon što sounds more neutral and is very common in everyday speech.

Why is there a comma after Pročitavši članak o politici?

Because Pročitavši članak o politici is an introductory subordinate phrase (a non-finite clause) that sets the circumstance for the main action.

In Croatian, such introductory verbal-adverb phrases are normally separated from the main clause by a comma:

Pročitavši članak o politici, mladi građanin je manje sumnjao...
Vrativši se kući, otišao je ravno na spavanje.
(Having returned home, he went straight to sleep.)

If the verbal-adverb phrase comes after the main clause, you also separate it with a comma:

Mladi građanin je manje sumnjao u budućnost države, pročitavši članak o politici.

Why is it mladi građanin, not mlad građanin or mladog građanina?

Several things are going on here:

Case and gender
- građanin is masculine, singular, nominative (it is the subject).
- The adjective must agree: mladi (masc. sg. nominative, long/definite form).
Long vs. short adjective forms
Croatian often has two forms for adjectives like mlad (young):
- mlad građanin – short/indefinite form
- mladi građanin – long/definite form
In modern standard language, mladi građanin is slightly more common here and can sound a bit more specific or formal (almost like the young citizen), while mlad građanin can feel a bit more neutral or descriptive (a young citizen). The difference is subtle and often they’re interchangeable.
Why not mladog građanina?
- mladog građanina would be genitive or accusative, but we need nominative for the subject.
- So mladog građanina would be used in contexts like:
  - Vidim mladog građanina. – I see the young citizen. (accusative)

How does word order work with je and manje in mladi građanin je manje sumnjao? Can I move them around?

Two key points:

je is a clitic (short, unstressed auxiliary) and Croatian clitics tend to stand in “second position” in the clause.
manje is a normal adverb, not a clitic, so its position is more flexible.

Your sentence:

Mladi građanin je manje sumnjao u budućnost države. – fully correct and natural.

Other acceptable orders:

Mladi građanin manje je sumnjao u budućnost države. – also very natural; a lot of speakers might actually prefer this.
Mladi je građanin manje sumnjao u budućnost države. – also grammatically fine; here je comes after the first stressed word (Mladi), still effectively in second position.

What you generally cannot do is leave out je in this past tense, or put je first in the sentence:

✗ Je mladi građanin manje sumnjao... – wrong in standard Croatian.
✗ Mladi građanin manje sumnjao... – wrong (missing the auxiliary je).

Why is it manje sumnjao, not something like imao manje sumnje?

The verb sumnjati means to doubt, to be suspicious, not to have doubts as a noun phrase. So:

sumnjati u nešto – to doubt something
manje sumnjati u nešto – to doubt something less

In your sentence, manje is simply a comparative adverb modifying the verb:

je manje sumnjao = he doubted less / he was less doubtful

You could express a similar idea with a noun:

imao je manje sumnje u budućnost države – he had fewer doubts about the future of the state

…but the original sentence with sumnjati is more direct and idiomatic for this structure.

Why do we say sumnjati u budućnost države with u + accusative, not o budućnosti or za budućnost?

This is governed by the verb sumnjati, which in this meaning normally takes the preposition u with accusative:

sumnjati u nešto – to doubt something / not trust in something

So:

sumnjati u budućnost države – to doubt the future of the state
- u budućnost – accusative
- države – genitive (of the state)

Alternatives with different prepositions would change the meaning:

sumnjati o nečemu – not idiomatic; you wouldn’t say it.
za budućnost države – usually links to other verbs, like boriti se za budućnost države (to fight for the future of the state), not sumnjati.

So for to doubt X, the natural pattern is sumnjati u X.

What cases are used in članak o politici and budućnost države?

članak o politici
- članak – nominative singular (subject of pročitavši’s action).
- o requires locative when it means “about”.
- politika (feminine noun) in locative singular becomes politici.
  → o politici = about politics
budućnost države
- budućnost – here accusative singular (object of sumnjati u). For this feminine noun, nominative and accusative singular look the same: budućnost.
- država – in države, we have genitive singular:
  - budućnost države = literally the future of the state.

So the structure budućnost + genitive is the standard way to say the future of X.

Does this sentence sound formal or neutral in Croatian?

Because of the past verbal adverb Pročitavši, the sentence has a slightly formal or literary flavor. It would fit well in:

written texts (essays, articles, literature)
more careful, educated speech

A more neutral, everyday version would more likely use a clause with kad or nakon što:

Kad je pročitao članak o politici, mladi građanin je manje sumnjao u budućnost države.
Nakon što je pročitao članak o politici, mladi građanin je manje sumnjao u budućnost države.

Both versions are correct; the original is just stylistically more elevated.