Answer:
The answer to the question: What did the caning of Charles Sumner in Congress highlight, would be: It showed the level of division that had been reached between the North and the South, Abolitionists vs. Slaveholders, and it became almost a prequel to what would later end up being the Civil War.
Explanation:
The Caning of Charles Sumner, also known as the Brooks-Sumner affair, was a deplorable event that took place in 1856, in the U.S Senate, when a Representative, Preston Brooks, took a cane to beat Senator Charles Sumner on the Senate floor to humiliate him, and demean him as less than a gentleman, for having dared to give a speech in favor of abolition and denouncing the cruelty of slaveholders. Since the language used by Sumner was deemed by the congressmen from the South, as disrespectful and ungentlemanly, Brooks asked a friend about dueling and finally came to the conclusion that someone inferior, like Sumner, did not deserve to be treated any better. So, he decided to cane Charles Sumner almost to death.
