kakakukousyou ga hazimatta.

It is read:

かかくこうしょう が はじまった。

Word by word:

• 価格 = かかく = price
• 交渉 = こうしょう = negotiation
• 価格交渉 = かかくこうしょう = price negotiation
• 始まった = はじまった = started / began

It is a compound noun made from two nouns:

• 価格 = price
• 交渉 = negotiation

Together, 価格交渉 means price negotiation or price negotiations.

This is very common in Japanese: two nouns are combined into one larger noun. So in this sentence, 価格交渉 acts as a single noun phrase.

が marks the thing that started.

So in:

価格交渉 が 始まった。

the price negotiation is the thing that began.

A natural way to think of it is:

• 価格交渉 = price negotiation
• が = marks what is doing the intransitive action
• 始まった = began

So the basic structure is:

[Something] が 始まった = [Something] started / began

This is an important verb pair:

• 始まる = to begin, to start by itself or as an event
• 始める = to begin/start something

In this sentence, the negotiation itself is what began, so Japanese uses the intransitive verb:

• 価格交渉が始まった。 = The price negotiation started.

If you used 始めた, you would need someone who started it:

• 彼らが価格交渉を始めた。 = They started the price negotiations.

So:

• 始まる → no direct object; the event begins
• 始める → someone starts something

始まった is the plain past form of 始まる.

Conjugation:

• dictionary form: 始まる
• past plain form: 始まった

This means began or started.

Because 始まる is a う-verb, the past tense changes like this:

• 〜る becomes 〜った

So:

• 始まる → 始まった

Japanese often leaves out information that is clear from context.

In English, you might say:

• The price negotiations started.
• Price negotiations have begun.

In Japanese, if the context already tells you what situation is being discussed, you can simply say:

価格交渉が始まった。

There is no need to explicitly say who is involved unless it matters.

Japanese very often omits:

• the subject
• the doer
• the listener-known context

So this sentence is perfectly natural even without saying who is negotiating.

Yes, but the nuance changes.

• 価格交渉が始まった。
  This presents the start of the price negotiation as the main event or new information.

• 価格交渉は始まった。
  This makes price negotiation the topic, with a nuance like as for the price negotiation, it has started.

In many contexts, が sounds more natural here because the sentence is simply reporting that something began.

A rough contrast:

• が = focuses on what started
• は = sets it up as the topic, often with contrast or broader context

It is in the plain style.

• 価格交渉が始まった。 = plain
• 価格交渉が始まりました。 = polite

The plain form is common in:

• written reports
• headlines
• narration
• casual conversation

Because the sentence is short and direct, it can sound a bit like a news report or business update.

It can correspond to any of those in English depending on context.

• started
• began
• has started

Japanese past tense does not always match English past tense one-to-one.

So:

価格交渉が始まった。

could be understood as:

• The price negotiations started.
• The price negotiations began.
• The price negotiations have begun.

The best translation depends on the situation and surrounding sentences.

Because 始まる is intransitive, it does not take a direct object marked by を.

Compare:

• 価格交渉が始まった。
  The negotiation started.

• 彼らが価格交渉を始めた。
  They started the negotiation.

So:

• が goes with 始まる
• を goes with 始める

This is a very common transitive/intransitive pattern in Japanese.

No. Normal Japanese writing would usually be:

価格交渉が始まった。

Spaces are often added in learning materials to make the structure easier to see, but standard Japanese does not usually separate words with spaces.

It sounds concise and factual.

Depending on context, it could sound like:

• a business update
• a news-style statement
• a narration of events

Because 価格交渉 is a somewhat formal/business-like expression, the whole sentence feels more like business Japanese or reporting language than casual everyday chat.

For example, it sounds more formal than something like:

• 値段の話し合いが始まった。

Both can refer to negotiating price, but 価格交渉 is the more formal and set expression.