Definition & Meaning of "sell somebody down the river"in English

What is the origin of the idiom "sell someone down the river" and when to use it?

The idiom "sell someone down the river" has its roots in the history of slavery in the United States. It dates back to the 19th century when it was used to describe a betrayal or a severe act of deception. In the context of slavery, "down the river" referred to the deep South, where conditions for enslaved people were often harsher. It implies that the betrayal is severe and often involves dire consequences for the individual being betrayed. This idiom emphasizes the feeling of being let down or placed in a difficult and disadvantageous position.