Meaning:
* American: This implies the person has embraced the ideals and values associated with the United States, often seen as a land of opportunity and fresh starts.
* Leaving behind... ancient prejudices and manners: This suggests a rejection of outdated and potentially harmful beliefs and behaviors. It implies that the person has shed the baggage of their past, possibly from their original culture or family traditions, and is embracing a new way of being.
Grammatical Issues:
* "Leaving behind" is a participle, and participles need to be linked to a noun. It should be "He is an American who is leaving behind him all his ancient prejudices and manners." This makes the sentence grammatically correct.
* The word "him" is redundant and can be removed. The sentence is clearer without it: "He is an American who is leaving behind all his ancient prejudices and manners."
Overall, the sentence suggests that America has the power to change people, allowing them to shed their past and embrace a new identity. It hints at the potential for personal growth and transformation that is often associated with American ideals.