〜以上（は）
Now that 〜以上は
Meaning
"Now that ~", "since ~" — given this fact, a duty or resolve follows.
Formation
[plain form] + 以上（は） · [noun] である + 以上（は）
Notes
The second clause states an obligation, a resolve or a strong judgement — なければならない, べきだ, つもりだ. It is a logical "given that", so it does not fit a plain description of cause; use から or ので for that. からには is a close synonym.
Examples
引き受（ひきう）けた以上（いじょう）は、最後（さいご）までやります。
Now that I have taken it on, I will see it through.
Breakdown
約束（やくそく）した以上（いじょう）、守（まも）らなければなりません。
Having promised, I must keep my word.
Breakdown
学生（がくせい）である以上（いじょう）、勉強（べんきょう）するべきです。
As long as you are a student, you ought to study.
Breakdown
日本（にほん）で働（はたら）く以上（いじょう）、日本語（にほんご）は必要（ひつよう）です。
If you are going to work in Japan, Japanese is essential.
Breakdown
試合（しあい）に出（で）る以上（いじょう）、勝（か）ちたいです。
Since I am playing in the match, I want to win.
Breakdown
⚠️ Often confused with
〜から
Reason 〜から (because)
Gives a reason or cause — "because ~ / since ~". Subjective and conversational. Comes afte...
〜ので
Reason 〜ので (formal because)
A more formal / softer "because" than から. Used in polite speech, business, and writing....
〜だけあって
As you would expect 〜だけあって
"As you would expect of ~", "no wonder, given that ~". Admiring.
〜ことから
Judging from 〜ことから
"From the fact that ~", "judging from ~" — states the evidence a conclusion rests on.
〜につき
Due to / per 〜につき
"Due to ~" in official notices; also "per ~" for rates.
〜ゆえ（に）
Owing to (literary) 〜ゆえ（に）
"Because of ~", "owing to ~" — a stiff, literary statement of cause.
〜とあって
Given the occasion 〜とあって
"Because it is (the special occasion of) ~" — a special situation produces a natural resul...
〜ばこそ
It is only because 〜ばこそ
"It is precisely because ~ (and nothing else)" — an emphatic, positive reason.
〜あっての
Made possible only by 〜あっての
"Which exists only thanks to ~", "~ is what makes it possible".
〜手前
With others watching 〜手前
"Since ~ (and with people watching), I have no choice but to ..." — social face forces the...
〜こととて
Seeing that (apologetic) 〜こととて
"Because it is ~ (please excuse it)" — a humble reason offered with an apology.
〜にかこつけて
Under the pretext of 〜にかこつけて
"Using ~ as an excuse", "under the pretext of ~".