EL DORADO SPRINGS, Mo.—The owner of the nicest restaurant in town doesn't serve alcohol, worried that his pastor would be disappointed if he did. Public schools try to avoid scheduling events on Wednesday evenings, when churches hold Bible study. And Democrats here are a rare and lonely breed.

Older, nearly 100% white and overwhelmingly Republican, El Dorado Springs is typical of what is now small-town America. Coffee costs 90 cents at the diner, with free refills. Two hours north and a world away in Kansas City, Starbucks charges twice that, and voters routinely elect Democrats.

There have always been differences between rural and urban America, but they have grown vast and deep, and now are an underappreciated factor in dividing the U.S. political system, say politicians and academicians.

Polling, consumer data and demographic profiles paint a picture of two Americas—not just with differing proclivities but different life experiences. People in cities are more likely to be tethered to a smartphone, buy a foreign-made car and read a fashion magazine. Those in small towns are more likely to go to church, own a gun, support the military and value community ties.

In many ways, the split between red Republican regions and blue Democratic ones—and their opposing views about the role of government—is an extension of the cultural divide between rural Americans and those living in cities and suburbs.