Andrew Lawler, writing for the New York Times:
Slaves laid the foundation for the American appetite for chicken, but it was the forced opening of China by the West in the 1840s that made the modern bird possible. American ships brought specimens of Asian chickens never seen in America. Breeders crossed the large and colorful exotics with their smaller but hardier Western counterparts to produce a bird that could lay more eggs and provide more meat. The results were famous varieties, like the Plymouth Rock and Rhode Island Red, that appeared just as the nation began to industrialize.
I had no idea about this history!