<p>To add on to an already adequate explanation:</p>
<p>This is one of those rare questions that contain idioms. Don’t try to figure out the place of “not to mention” – its place doesn’t make much sense because it is an idiom. When you say “not to mention” after a comma, it does not have to modify the object. “Mention” is a verb done by a narrator (the person saying the sentence), so it is simply an extension of what is previously said. </p>
<p>So, the only thing that has to take precedence is that the two clauses are related, in meaning, to each other: “[To mention] [this]…, not to mention [that]”</p>
<p>dictionary examples:
“Gaining weight didn’t help her health, not to mention the high blood pressure that ran in her family.”
“They don’t have any of the players from that championship team anymore, not to mention manager Casey Stengel.”</p>
<p>Bolded are the associated nouns in each sentence, the first of which is the reference point.</p>
<p>“Gaining weight, one factor, didn’t help her health, nor did another factor, the high blood pressure in her family.”</p>
<p>“They don’t have any of these players, nor did they have another player, Casey Stengel.”</p>
<p>CORRECT:
</p>
<p>Since “on” is repeated, we know immediately that that is the reference point.</p>
<p>The introduction of the chili pepper had a tremendous impact on the balance of power in particular countries
The introduction of the chili pepper had a tremendous impact on other particular cultures</p>
<p>Now if you say “an impact also on” instead of “not to mention,” you are not utilizing the idiom whose purpose cannot be said within grammatical (correct) terms.</p>
<p>INCORRECT:
</p>
<p>X had an impact on Y, an impact also on Z.</p>
<p>First of all, the impact of X on Y is not the same as the impact of X on Z. Therefore, you cannot say “an impact also on Z”</p>
<p>Second of all, when you separate two nouns with a comma, those two nouns are presumably of the same importance. In other words, as opposed to “not to mention,” an unidiomatic phrase is restricted.</p>
<p>I gave it to Mary, a person that never gives -> Mary never gives</p>
<p>X had an impact on Y, an impact also on Z.
This says that Y had an impact on Z, which is not true</p>