After 1940, Owsley and his wife Harriet pioneered what came to be called the "new social history". They studied the historical demography of the South and social mobility and produced a history called "Plain Folk of the Old South". Historian Vernon Burton described it as "one of the most influential works on Southern history ever written." The Owsleys culled data from federal census returns, tax and trial records, and local government documents and wills. In "Plain Folk", they argued that Southern society was not dominated by planter aristocrats, but that yeoman farmers played a significant role. The religion, language, and culture of white common people created a democratic "plain folk" society, Owsley argued.