America didn't always have a middle class.
In the late 1700s and early 1800s, the foundling nation had wealthy landowners, but everyone else was pretty close together, both physically and economically, said historian Stuart Blumin.
Mr. Blumin, a retired history professor at Cornell University and author of the 1989 book "The Emergence of the Middle Class," said the more egalitarian society of the first 50 years of the United States had a lot to do with how goods were created.
Most products were made by artisans who often had apprentices living in their households, and they both lived within a short distance of their wealthier customers.
Then, in the 1820s, all that began to change.
Goods such as textiles and shoes began to be produced in "manufactories," and eventually those laborers started living next to each other, forming the first working-class neighborhoods.
At the new factories, some employees were hired to oversee the others or to work in the office. Then came the separation of where products were made and where they were sold, which led to an explosion of retail stores in cities around the nation throughout the 1800s.
As these stores evolved, they became a magnet for women shoppers, he said, and so "now, what is the owner wearing? Not a leather apron as he once would have, but a suit. And who else is there? Wage-earning clerks."
As time went on, these "white-collar workers" and entrepreneurs began to make more money than manufacturing employees, which allowed them to settle in better neighborhoods of their own.
As white-collar and working-class employees began to separate geographically, they also went to different churches, social clubs and taverns. Even the independent baseball clubs that became a mania in the late 1800s were split by class, he said.
Victorian middle-class homes became the domain of women, who entertained guests in the parlor, educated and raised the children and governed the family's social life.
"This was often hard on the men of that era," he said, "because women were starting to make them behave themselves, to stop eating peas with their knives and telling lewd stories and spitting tobacco juice on the new Brussels carpet."
As America entered the 20th century, the story of the middle class became more complex, Mr. Blumin said.
The growth of labor unions moved some blue-collar workers up the income ladder toward middle-class lifestyles, while the development of department stores and other large offices led to a "white-collar proletariat."
"They may have been salary earners," Mr. Blumin said, "but their pay was very low, their work was tedious, they were in large organizations."
These new white collar masses "had very little chance for promotion or entrepreneurship," he said, "and so more and more, in insurance and shipping and banking companies, as office work expanded and the typewriter prevailed, women become more and more pervasive and they were paid less."
As the 20th century wore on, two major events reshaped the middle class -- the Great Depression, which plunged millions into poverty, and World War II, which sent millions of men overseas and ushered even more women into the workforce.
Some economists trace the modern middle class to critical government decisions that were made as the nation emerged from the world war.
One was the G.I. Bill, which raised the educational level of millions of veterans at bargain rates. Mr. Blumin, who wrote a book about that program, said many Americans don't realize that the bill helped more veterans with non-college training than it did with university education`.
"About 2.2 million people went to college under the G.I. Bill, but 5.6 million had sub-college training," he said. "And a lot of those classes were in the emerging technical jobs in society, like auto repair or TV and radio repair."
The other major federal initiative was subsidy programs to help returning veterans become homeowners. The Federal Housing Administration, which had been set up in the middle of the Depression, helped spur the construction of thousands of new suburban houses with its mortgage insurance programs, and those housing developments were increasingly linked to major cities by the fast-growing Interstate Highway System.
These policies helped build a strong middle class, but one other major development -- easier credit for middle-income Americans over the past 40 years -- has had mixed blessings.
On one hand, it has allowed people to get mortgages and make major consumer purchases more easily. On the other hand, it has created serious debt problems for millions of Americans and played a critical role in the recent housing collapse.
Sylvia Allegretto, a research economist at the University of California at Berkeley, said the expansion of credit has created two middle classes.
"I've always lived below my means," said Ms. Allegretto, who grew up in Western Pennsylvania as the daughter of a union painter and a factory worker, "but I have friends who always have the latest gadgets and cars, which is why we collectively have so much debt, right?
"And when I went to college, there also weren't credit card companies sitting out there waiting to hand you a free credit card the minute you walked in the door. There is a different culture out there today."
The Berkeley economist also worries that many of today's younger middle-class families do not have the same sense of social cohesion and shared values that their parents and grandparents had.
"I think that those older generations had more of a sense of community as Americans, both a sense of the victory after the war and coming out of the Depression.
"After the Depression, we had the Federal Deposit Insurance Corporation that prevented runs on the banks, we had unemployment insurance -- and people knew these things were going to help them, because they had just come out of the Depression where they didn't have those things."
Correction/Clarification: (Published November 21, 2011) A photo of a group of women surrounding a Buick in 1952 was taken along the Allegheny River. A caption accompanying the photo Sunday as part of the Middle of Nowhere series gave an incorrect location.
Mark Roth: firstname.lastname@example.org or 412-263-1130.