〜ため(に) (because)
because of, due to (formal)
Noun + のため(に) · Plain form + ため(に) (な-adj + な)
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At N4, ために meant "in order to". The same word also gives a cause, in a formal, neutral way: 大雪のため、電車が止まっています, "trains are stopped due to heavy snow".
You'll meet it in announcements, news, notices and business writing. In conversation, から and ので are far more common.
How do you tell the two meanings apart? Purpose needs a verb someone chooses to do, and usually the dictionary form: 合格するために勉強する. A cause is often a past event, a state or a noun: 事故があったため, 体調が悪いため.
The に is optional in the cause meaning, and is often left off: 工事のため、通れません.
Examples
大雪のため、電車が止まっています。
Trains are stopped due to heavy snow.
事故があったため、道が込んでいる。
The roads are busy because there was an accident.
工事のため、この道は通れません。
This road is closed due to construction work.
体調が悪いため、今日は休みます。
I'll be off today as I'm not feeling well.
台風のために、飛行機が遅れた。
The flight was delayed because of the typhoon.