Social class is an important theme for historians of the United States fordecades. The subject touches on many other elements of American history such as that of changing U.S. education, with Greater education attainment leading to expanding household incomes for many social groups. The overall level of prosperity grew greatly in the U.S. through the 20th century as well as the 21st century, anchored in changes such as growing American advances in science and technology with American inventions such as the phonograph, the portable electric vacuum cleaner, and so on. Yet much of the debate has focused lately on whether social mobility has fallen in recent decades as income inequality has risen, what scholars such as Katherine S. Newman have called the "American nightmare." For most of American history, social class barriers were fundamentally rigid, with various private and public institutions enforcing rules based on racial segregation and other forms of classifying people based on prejudices such as antisemitism and Hispanophobia. All this changed greatly with the rise of broad-based prosperity in the aftermath of World War II and efforts to expand Constitutional civil rights under the law to groups such as African-Americans and Hispanic-Americans. Issues regarding social class have remained hot-button topics in U.S. politics, with the American Great Recession causing massive socio-economic harm across the country from southerners to northerners to working-class whites to middle-class blacks Colonial period Historians in recent decades have explored in microscopic detail the process of settling the new country and creating the social structure. Southern colonies The main themes have been the class system of the plantation South. These include the plantation masters and their families, as typified by the Byrd family. The plantation elite in gen regions of the Chesapeake, with some attention to South Carolina as well. The region had very few urban places apart from Charleston, where a merchant elite maintained close connections with nearby plantation society. It was a goal of prosperous merchants, lawyers and doctors in Charleston to buy lands and retire as country gentlemen. Charleston supported diverse ethnic groups, including Germans and French, as well as a free black population. Beyond the plantations yeoman farmers operated small holdings, sometimes with a slave or two. Missionaries commented on their lack of religiosity. The plantation areas of Virginia were integrated into the vestry system of the established Anglican church. By the 1760s a strong tendency to emulate British society