Wojna trwała pięć lat.

Because in Polish past tense, the verb agrees with the subject in gender and number.

• wojna = war
• wojna is a feminine singular noun

So the past tense of trwać must also be feminine singular:

• masculine: trwał
• feminine: trwała
• neuter: trwało

Since the subject is wojna, we get Wojna trwała.

The basic dictionary form is trwać.

trwać means to last, to continue, or to go on.
In this sentence, trwała is the past tense form.

So:

• trwać = to last / continue
• trwała = lasted / was continuing

In Polish, duration is normally expressed with verbs like trwać rather than with a structure like English was for.

So Polish says:

• Wojna trwała pięć lat.

Literally, this is closer to:

• The war lasted five years.

That is the natural way to express duration in Polish.

Because after the numbers 5 and above, Polish nouns usually take the genitive plural.

The noun is:

• rok = year

Its forms include:

• singular nominative: rok
• plural nominative: lata
• genitive plural: lat

After pięć (five), Polish uses lat, not lata:

• pięć lat = five years

This is a very important pattern:

• jeden rok = one year
• dwa lata = two years
• trzy lata = three years
• cztery lata = four years
• pięć lat = five years
• sześć lat = six years

Because Polish often expresses duration directly, without a preposition.

So:

• Wojna trwała pięć lat. = The war lasted five years.

This is completely normal Polish.

You can sometimes also see przez in other duration expressions, but with trwać it is very natural to say simply:

• trwać godzinę
• trwać tydzień
• trwać pięć lat

So no extra word is needed here.

Wojna is in the nominative case, because it is the subject of the sentence.

The subject is the thing doing the action or being described. Here, the sentence is about the war, so:

• wojna = nominative singular

That nominative subject also determines the verb agreement, which is why we get feminine trwała.

It comes from the imperfective verb trwać.

That makes sense because trwać describes a process or state extending through time: something continues or lasts.

For duration, Polish typically uses an imperfective verb, because the focus is on the span of time, not just the completed endpoint.

So Wojna trwała pięć lat presents the war as something that continued for five years.

Yes. Polish word order is more flexible than English because endings carry a lot of grammatical information.

The neutral order here is:

• Wojna trwała pięć lat.

But other orders are possible for emphasis, for example:

• Pięć lat trwała wojna.
• Trwała wojna pięć lat. (less neutral, more stylistic)

These alternatives can sound more literary, contrastive, or emphatic.
For a learner, Wojna trwała pięć lat is the safest and most natural basic order.

A rough pronunciation is:

• trva-wa

A few key points:

• trw is pronounced with a real v sound: trv...
• ała sounds roughly like awa
• Polish ł is pronounced like English w

So trwała sounds roughly like TRVA-wa.

And the whole sentence is approximately:

• VOY-na trva-wa pyench lat

That is only an approximation, but it helps with the main sounds.

Yes, many learners find pięć tricky.

Important points:

• pię- contains a nasal vowel written ę
• before ć, it is often pronounced something like pyen or pyench
• ć is a soft sound, a bit like a very soft ch/t sound

A rough English-friendly approximation is:

• pyench

Not perfect, but close enough to start.

Yes, depending on context.

Because trwać is imperfective, the sentence can simply state the duration of something in the past:

• The war lasted five years

In the right context, it can also carry a more descriptive sense:

• The war was going on for five years

But in ordinary translation, lasted five years is usually the most natural choice.

The pattern happens with many time expressions, though each noun has its own forms.

Examples:

• pięć lat = five years
• pięć miesięcy = five months
• pięć tygodni = five weeks
• pięć dni = five days
• pięć godzin = five hours

So the general idea is the same: after 5+, Polish usually uses a form corresponding to the genitive plural.
But the actual ending depends on the noun, so you need to learn each noun’s plural pattern.