なぜなら is to emphasise (Why?) and から is the because part, so both are needed from my understanding
The answer is yes, it is. With なぜなら/なぜかというと, you are emphasizing a reason, which has to be followed by a から for your statement to make sense.
I don’t know if there’s a good article in English so this may be somewhat hard to read depending on your level but this sort of thing is called [呼応](#fg “こおう”)の[副詞](#fg “ふくし”) and [here](https://xn--3kq3hlnz13dlw7bzic.jp/concord/) is a page with a good few examples
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なぜなら is to emphasise (Why?) and から is the because part, so both are needed from my understanding
The answer is yes, it is. With なぜなら/なぜかというと, you are emphasizing a reason, which has to be followed by a から for your statement to make sense.
I don’t know if there’s a good article in English so this may be somewhat hard to read depending on your level but this sort of thing is called [呼応](#fg “こおう”)の[副詞](#fg “ふくし”) and [here](https://xn--3kq3hlnz13dlw7bzic.jp/concord/) is a page with a good few examples