Горе изменило всю семью.

Because the subject is горе, and горе is a neuter singular noun in Russian.

In the past tense, Russian verbs agree with the subject in gender and number:

• masculine: изменил
• feminine: изменила
• neuter: изменило
• plural: изменили

So:

• горе изменило = grief changed

Even though горе refers to something abstract, it is still grammatically neuter.

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

In Горе изменило всю семью, the thing doing the action is горе.

So the structure is:

• горе = subject, nominative
• изменило = verb
• всю семью = direct object, accusative

Because всю семью is the direct object of the verb изменило, so it must be in the accusative case.

Dictionary form:

• вся семья = the whole family / the entire family

Accusative form:

• всю семью

Both words change:

• вся → всю
• семья → семью

This is normal for a feminine singular noun and its modifier.

Here изменить means to change, to alter, or to transform.

So Горе изменило всю семью means that grief had a strong effect and made the family different.

A learner may know that изменить can also mean to betray or to cheat on someone, but that is a different usage.

Compare:

• Горе изменило всю семью. = Grief changed the whole family.
• Он изменил жене. = He cheated on his wife.

So the meaning depends on the structure and context.

Изменило comes from the perfective verb изменить.

The perfective aspect is used because the sentence presents the change as a completed result:

• grief came
• it had an effect
• the family ended up changed

If you used the imperfective изменяло, it would suggest an ongoing, repeated, or process-focused action:

• Горе изменяло всю семью = grief was changing the whole family

That is possible in some contexts, but изменило is more natural if you mean the family was changed as a result.

Горе usually suggests deep grief, sorrow, often connected with tragedy, loss, or serious suffering.

It is stronger and heavier than:

• грусть = sadness, melancholy
• печаль = sorrow, sadness, sadness with a literary or emotional tone

So in this sentence, горе gives a strong emotional sense: this is not just mild sadness, but something serious that affected the whole family.

Yes. Russian word order is more flexible than English word order.

The neutral order here is:

• Горе изменило всю семью.

But other orders are possible, depending on emphasis:

• Всю семью изменило горе.
  Emphasis on the whole family
• Изменило всю семью горе.
  More literary or dramatic

Even when the order changes, the cases still show who is doing what:

• горе is nominative = subject
• всю семью is accusative = object

Russian does not have articles like a or the.

So:

• горе can mean grief or the grief, depending on context
• всю семью can mean the whole family

Russian usually expresses definiteness through context, word order, and the overall situation rather than with articles.

You certainly can say Горе изменило семью.

But всю adds the idea of the whole / entire family. It emphasizes that the grief affected everyone in it, not just one person or part of the family.

Compare:

• Горе изменило семью. = grief changed the family
• Горе изменило всю семью. = grief changed the whole family

So всю makes the statement stronger and more complete.

The main stress is:

• Го́ре измени́ло всю́ семью́.

A rough pronunciation guide:

• Го́ре = GO-rye
• измени́ло = eez-mye-NEE-luh
• всю = roughly fsyu
• семью́ = sye-MYU

A few useful notes:

• всю begins with a consonant cluster that can feel difficult for English speakers.
• семью contains the ью ending, which is also worth practicing carefully.
• Final stress matters a lot in Russian, so семью́ should be stressed on the last syllable.

It is singular.

Even though a family contains multiple people, семья is grammatically one noun, so Russian treats it as singular:

• вся семья = the whole family
• семья была = the family was

In this sentence, семью is just the singular accusative form of семья.