nothing but, nothing other than
Used to emphasize that something is the only explanation or reason for a situation.
Examples
これは彼の努力にほかならない。
This is nothing but his effort.
成功の要因はチームの団結にほかならない。
The reason for success is nothing but the team's unity.
彼女の敗北は油断にほかならない。
Her defeat is nothing but carelessness.
Quick check
これは彼の努力___。