N3
ために
Due to, Because of, As a result of
空手の試合で負けたために、毎日夜遅くまで練習するようになった。
Because I lost the karate match, I started practicing until late every night.
Explanation
「～ために」 (cause) means 'because of' and states a cause objectively, mostly in writing, news and formal speech. The first part is often beyond anyone's control, such as a disaster, an accident or an established fact, and the second part is its result: 「大雪のために、飛行機が欠航となった」 (Flights were canceled because of heavy snow), 「事故のために、電車が遅れている」 (The train is late because of an accident).
Mixed up with
The second part can't be your will, a wish, an order or an invitation. Don't say 「×雨が降ったために、傘を買おう」.
Telling cause from purpose: past 「～たために」, and non-volitional verbs or adjectives like 「暑いために」, are always cause. If the second part is a deliberate act it is purpose; if it is a fact or accident it is cause.
「から」 is subjective and can be followed by an order or request; 「ので」 is objective and polite; 「ために」 is the stiffest and most written.