Los hermanos dejaron de pelear.

Because los hermanos means the brothers / the siblings: a specific group.

In Spanish, the definite article el / la / los / las is used a lot, and here it tells us we are talking about particular people, not brothers in general.

• Los hermanos = the brothers / the siblings
• Hermanos by itself would usually sound incomplete in this sentence.

Also, hermanos is masculine plural, which can mean:

• a group of brothers, or
• a mixed group of siblings (brothers and sisters)

So the exact meaning depends on context.

It can mean either, depending on context.

In Spanish, the masculine plural often works as the mixed-gender plural too. So:

• los hermanos can mean the brothers
• but it can also mean the siblings if the group includes sisters

If Spanish wants to be fully explicit about a mixed group, it could say los hermanos y las hermanas, but that is often unnecessary.

Dejar de + infinitive is a very common Spanish structure meaning to stop doing something.

So:

• dejar de = to stop
• pelear = to fight
• dejaron de pelear = they stopped fighting

This is a fixed pattern:

• dejar de hablar = to stop talking
• dejar de correr = to stop running
• dejar de fumar = to stop smoking

So the de is not optional here.

Because dejar de + infinitive is the standard expression for stopping an action.

Without de, the meaning changes.

Compare:

• dejaron de pelear = they stopped fighting
• dejaron pelear = they let someone fight / they allowed fighting

So de is essential. It tells you this is the stop doing something structure, not the verb dejar meaning to leave or to allow.

Dejaron is the preterite, which usually presents the action as completed: they stopped fighting at some point.

So Los hermanos dejaron de pelear sounds like:

• there was fighting
• then it stopped

That is a complete event.

If you used dejaban, that would be the imperfect, which usually gives a background, habitual, or unfinished sense. In many contexts it would sound less natural here unless there is more information.

Compare:

• dejaron de pelear = they stopped fighting
• dejaban de pelear cuando... = they would stop fighting when... / they were stopping fighting when...

For a simple main statement about what happened, dejaron is the normal choice.

It is the third person plural preterite of dejar.

Breaking it down:

• infinitive: dejar
• preterite stem used regularly: dej-
• ending for ellos / ellas / ustedes in the preterite: -aron
• so: dejaron

It means they left, they allowed, or here, as part of dejar de + infinitive, they stopped.

Because after dejar de, Spanish normally uses an infinitive.

This is similar to English patterns like:

• to stop fighting
• to keep talking
• to want to leave

In Spanish:

• dejar de pelear
• seguir hablando
• querer salir

So pelear stays in the infinitive because it is the action being stopped.

Yes, but it means something different.

• Los hermanos dejaron de pelear = The brothers/siblings stopped fighting
• Los hermanos se pelearon = The brothers/siblings had a fight / got into a fight

So se pelearon focuses on the fight happening. dejaron de pelear focuses on the fight ending.

You may also hear pelearse in Spanish for fighting with each other, but pelear on its own is also very natural here.

Because pelear can already work without se.

• pelear = to fight
• pelearse = to fight with each other / to fall out / to quarrel

In many contexts, both can be possible, but they are not always identical in tone.

Here, dejaron de pelear is perfectly natural and simply means they stopped fighting.

A version with se would usually be:

• Los hermanos dejaron de pelearse

That also makes sense, but it sounds a bit more explicitly like fighting with each other rather than fighting in a more general sense.

It can cover both, depending on context.

Pelear is a broad verb that can refer to:

• physical fighting
• arguing or quarrelling

So Los hermanos dejaron de pelear could mean:

• they stopped physically fighting, or
• they stopped arguing

The surrounding context tells you which one is meant.

Because dejar de + infinitive is the most standard and idiomatic way to say stop doing something in many cases.

Spanish does have parar de + infinitive, and in some regions or contexts it is used, especially in expressions like:

• No para de hablar = He/She never stops talking

But dejar de + infinitive is very common and neutral for saying that an action ceased.

So dejaron de pelear is a very natural choice.

A careful Spain pronunciation would be roughly:

los er-MA-nos deh-HA-ron deh peh-leh-AR

A few useful points:

• h in hermanos is silent
• j in dejaron has a strong throaty sound in Spain
• r in hermanos is a tapped r
• pelear has three vowel sounds: pe-le-ar

In IPA, a common pronunciation is approximately:

[loz eɾˈmanos deˈxaɾon de peleˈaɾ]

In much of Spain, los may sound like loz before the vowel in hermanos because the s links into the next word.

Not by itself. It simply says that they stopped fighting at that point.

The sentence does not automatically tell you whether:

• they stopped temporarily, or
• they stopped for good

For forever, Spanish would need extra wording, such as:

• Los hermanos dejaron de pelear para siempre = The siblings stopped fighting forever

So the basic sentence only tells you the fighting stopped.