〜にほかならない
is nothing other than, is precisely
Noun / から + にほかならない
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にほかならない asserts strongly that something is exactly this and nothing else: 成功したのは、努力の結果にほかならない, "the success is nothing other than the result of hard work". ほか means "other", so it's "it doesn't become anything other than".
It's common after から, to insist on a reason: 親が厳しいのは、子どもを愛しているからにほかならない, "parents are strict precisely because they love their children".
It's formal and emphatic, typical of essays, speeches and opinion pieces. It's often written に他ならない.
Compare にすぎない, "merely", which plays things down, and に違いない, "must be", which is a guess. にほかならない isn't a guess; it's a firm claim.
Examples
成功したのは、努力の結果にほかならない。
The success is nothing other than the result of hard work.
親が厳しいのは、子どもを愛しているからにほかならない。
Parents are strict precisely because they love their children.
これは差別にほかならない。
This is nothing short of discrimination.
彼の行動は、責任からの逃げにほかならない。
His behaviour is simply running away from responsibility.
今日の私があるのは、先生のおかげにほかならない。
I owe who I am today entirely to my teacher.