“When I started to read...about them, I realized they were this...enormous force of nature...who determined how the West opened." Author S.C. Gwynne's on what inspired his new book. In an NPR interview about Empire of the Summer Moon, Gwynne says it's undeniable that the Comanches were incredibly warlike. “They swept everyone off the Southern plains. They nearly exterminated the Apaches.” “They were the ones who stopped the Spanish from coming North," he explains. "Why did the French stop coming west from Louisiana? Comanches. ... Here was why the West Coast and the East Coast settled before the middle of the country."