The title is a slam on American society. Bigger Thomas, the novel’s main character, is a "native son" of America: he was born and raised as a black man in the U.S., so he’s a product of the country. Local cultural and social forces shaped and created him.
So if he’s a monster, the title suggests, it can be blamed on American society. And this is precisely what Max, Bigger’s lawyer, argues in Bigger’s defense after Bigger commits murder—twice.