zyuutai no sei de, yakusoku ni okuremasita.

It means because of the traffic jam or due to the traffic jam.

• 渋滞 = traffic jam / congestion
• のせいで = because of, due to, as a result of

So 渋滞のせいで、約束に遅れました。 means something like:

I was late for my appointment because of the traffic jam.

Yes. せい often implies that something caused a bad, annoying, or undesirable result.

In this sentence, being late is a negative result, so せいで fits well.

Compare:

• 雨のせいで、試合が中止になった。
  Because of the rain, the game was canceled.
  → negative/unfortunate result

A more neutral alternative is ために:

• 渋滞のために、約束に遅れました。
  This is more formal and less blame-like.

So せいで sounds a bit like it was the traffic jam’s fault.

The の connects the cause noun to せい.

Structure:

• Noun + のせいで

Examples:

• 雨のせいで = because of the rain
• 渋滞のせいで = because of the traffic jam
• 寝不足のせいで = because of lack of sleep

You can think of it as the noun modifying せい.

約束 can mean both promise and appointment, depending on context.

Here, because the sentence says 約束に遅れました (was late for ...), it means appointment, meeting, or arrangement.

So here it is not promise in the abstract sense. It is more like:

• an appointment
• a planned meeting
• something you arranged with someone

Because 遅れる often takes に to mark what you are late for.

Pattern:

• X に 遅れる = to be late for X

Examples:

• 学校に遅れる = be late for school
• 会議に遅れる = be late for a meeting
• 約束に遅れる = be late for an appointment / arrangement

So 約束に is the thing the speaker was late for.

No, that would not be natural.

With 遅れる, Japanese normally uses に, not を, for the thing you are late for.

So:

• 約束に遅れました = natural
• 約束を遅れました = unnatural / incorrect

This is something you mostly have to learn with the verb.

遅れました is the polite past form of 遅れる.

Breakdown:

• dictionary form: 遅れる
• polite non-past: 遅れます
• polite past: 遅れました

So the sentence is polite and refers to something that already happened.

A plain-form version would be:

• 渋滞のせいで、約束に遅れた。

遅れる is an intransitive verb.

It means:

• to be late
• to fall behind
• to not make it on time

Since it is intransitive, it describes the subject’s state rather than taking a direct object.

That is why the sentence is about being late, not delaying something.

For comparison:

• 電車に遅れた = I was late for the train
• 授業に遅れた = I was late for class

Japanese often leaves out the subject when it is understood from context.

So 渋滞のせいで、約束に遅れました。 does not explicitly say I, he, she, etc.

In many everyday situations, it would naturally mean:

• I was late for my appointment because of the traffic jam.

But depending on context, it could also mean someone else was late.

Yes, you can, and it is natural.

• 渋滞で = because of the traffic jam
• 渋滞のせいで = because of the traffic jam / because the traffic jam caused it

The version with のせいで puts more focus on the traffic jam as the cause, often with a slightly stronger negative or blaming nuance.

So:

• 渋滞で遅れました = neutral, common
• 渋滞のせいで遅れました = a bit more like I was late because of that traffic jam

Sometimes yes, but not always.

• 遅れる = to be late
• 遅刻する = to be tardy / to arrive late

遅刻する is often used for being late to school, work, class, etc.

Examples:

• 学校に遅刻しました = I was late for school
• 会社に遅刻しました = I was late for work

With 約束, 遅れました sounds more natural:

• 約束に遅れました = natural
• 約束に遅刻しました = understandable, but less natural in many contexts

So for this sentence, 遅れました is a very good choice.

It is polite, but not extremely formal.

Why:

• 遅れました is polite ます form
• のせいで is ordinary everyday Japanese

So this sentence is appropriate in many normal situations, such as explaining why you were late.

If you wanted a more formal or business-like version, you might say:

• 渋滞のため、約束に遅れました。
• 渋滞のため、待ち合わせに遅れました。

These sound a little more formal and less emotional than のせいで.