What it means
他ならない follows a noun phrase with に and emphatically identifies something as exactly that and nothing else. It is commonly used to state the true cause, source, nature, or identity of something, often in formal explanations, essays, reports, and speeches. The expression carries stronger exclusivity and certainty than a simple copular statement.
Usage note
他ならない is relatively formal and is especially common in written or carefully prepared language. Its conventional polite counterpart is 他なりません; this is a polite form of the same construction, not an equivalent use of です. Do not confuse the construction with まさに, which is an adverb with a different function.
How to use it
この成果は、チーム全員の協力の結果に他なりません。
This achievement is nothing other than the result of the cooperation of every member of the team.
この成果は、チーム全員の協力の結果に他ならない。
This achievement is nothing other than the result of the cooperation of every member of the team.