Forræderiet endrer historien.

Because -et is the definite ending for many neuter nouns in Norwegian.

• et forræderi = a betrayal / a treasonous act
• forræderiet = the betrayal

So forræderiet is not a different word; it is the same noun in the definite singular form.

For the same reason: historien is the definite singular form of historie.

• en historie = a story / a history
• historien = the story / the history

The ending -n marks definiteness here because historie is a common-gender noun.

So the sentence uses the betrayal and the history/story, not a betrayal and a history/story.

Endrer is the present tense of å endre (to change).

Examples:

• å endre = to change
• endrer = changes / is changing
• endret = changed

So Forræderiet endrer historien means The betrayal changes the history/story in the present tense.

In Norwegian, verbs usually do not change form for different persons the way they do in English.

For example, with å endre in the present tense:

• jeg endrer = I change
• du endrer = you change
• han/hun endrer = he/she changes
• vi endrer = we change

So Norwegian does not add a special -s for he/she/it like English does. The form endrer stays the same.

Yes. This is the normal Norwegian main-clause word order:

Subject + Verb + Object

• Forræderiet = subject
• endrer = verb
• historien = object

So:

• Forræderiet endrer historien.

That is the standard neutral order for a statement.

You can say it grammatically, but it means something different.

• Forræderiet endrer historien = The betrayal changes the history/story
• Historien endrer forræderiet = The history/story changes the betrayal

Because Norwegian relies on word order, swapping the nouns usually changes who is doing the action.

Forræderi is a neuter noun.

That is why it uses:

• et forræderi = a betrayal
• forræderiet = the betrayal

A lot of Norwegian nouns ending in -eri or -i are neuter, but you still need to learn each noun individually.

Historie is usually treated as a common-gender noun.

So you get:

• en historie = a story / a history
• historien = the story / the history

In Bokmål, many nouns are either masculine or feminine, but a lot of learners first learn the common-gender-style pattern with en and -en.

In Norwegian, definiteness is often built into the noun itself by adding an ending.

Compare:

• English: the betrayal

• Norwegian: forræderiet

• English: the history/story
• Norwegian: historien

So instead of putting a separate word before the noun, Norwegian often marks the with a suffix:

• -en
• -et
• -a (in some feminine forms)

It can depend on context. Historie can mean both history and story.

So historien may mean:

• the history
• the story

Without context, both are possible. A learner should know that Norwegian historie covers both ideas more broadly than English sometimes does.

It would be:

Et forræderi endrer en historie.

That means:

• A betrayal changes a history/story

But this sounds less natural in many contexts, because the original sentence with definite forms feels more specific and complete:

• Forræderiet endrer historien. = The betrayal changes the history/story.

A rough guide is:

• forræderiet ≈ for-REH-de-ri-et
• historien ≈ his-TO-ri-en

A few notes:

• æ sounds somewhat like the vowel in English cat, though not exactly the same.
• The r is pronounced more clearly than in many English accents.
• The ending -et in forræderiet is pronounced as part of the word, not as a separate English-style the.

Exact pronunciation varies by dialect, but that rough shape is a helpful starting point.

Not in this sentence as it stands.

In ordinary Norwegian, if there is no adjective, you usually just use the noun with its definite ending:

• forræderiet
• historien

If you add an adjective, then Norwegian often uses double definiteness:

• det store forræderiet = the great betrayal
• den lange historien = the long story

So in the original sentence, forræderiet and historien are exactly what you would expect.