pros·per·i·ty  –noun, plural -ties.
1. a successful, flourishing, or thriving condition, esp. in financial respects; good fortune.
2. prosperities, prosperous circumstances.

Up until the early 1900s we were an agrarian society. Farming and ranching and fishing and trapping and mining were what most people did. In the larger towns and cities there were bankers and shop keepers.   How one was doing had more to do with the amount of land one owned or the size of ones shop or fishing fleet etc.  Nearly everything was made by hand. Factories, as we came to know them, did not really exist much. From the clothes on your back to the plow in your barn, most things were made one at a time by a few people.  Not the hundreds that were to be employed by big corporations.

The industrial revolution changed all that. With inventions and machinery previously unheard of. In fact the time from 1869 to 190 was know as the Gilded Age.

In American history, the Gilded Age refers to the era of rapid economic and population growth in the United States during the post-Civil War and post-Reconstruction eras of the late 19th century (1869-1896). The term "Gilded Age" was coined by Mark Twain and Charles Dudley Warner in their 1873 book, The Gilded Age: A Tale of Today. The name refers to the process of gilding and is meant to make fun of ostentatious display.

The Gilded Age is most famous for the creation of a modern industrial economy. During the 1870s and 1880s, the U.S. economy grew at the fastest rate in its history, with real wages, wealth, GDP, and capital formation all increasing rapidly. A national transportation and communication network was created, the corporation became the dominant form of business organization, and a managerial revolution transformed business operations. By the beginning of the 20th century, per capita income and industrial production in the United States led the world. The businessmen of the Second Industrial Revolution created industrial towns and cities in the Northeast with new factories, and hired an ethnically diverse industrial working class, many of them new immigrants from Europe. The super-rich industrialists and financiers such as Cornelius Vanderbilt, John D. Rockefeller, Andrew W. Mellon, Andrew Carnegie, Henry Flagler, J.P. Morgan and the prominent Astor family were attacked as "robber barons" by critics, who believed they cheated to get their money and lorded it over the common people.^[1] There was a small, growing labor union movement led especially by Samuel Gompers, head of the American Federation of Labor (AFL) after 1886.

Gilded Age politics, called the Third Party System, featured very close contests between the Republicans and Democrats, and, occasionally, third parties. Nearly all the eligible men were political partisans and voter turnout often exceeded 90% in some states.^[2]

The wealth of the period is highlighted by the American upper class' opulence, but also by the rise of American philanthropy (referred to by Andrew Carnegie as the "Gospel of Wealth") that used private money to endow thousands of colleges, hospitals, museums, academies, schools, opera houses, public libraries, symphony orchestras, and charities.^[3] John D. Rockefeller, for example, donated over $500 million to various charities, slightly over half his entire net worth.

All these new inventions and products and industries created quite a boom and most people did quite well.  America it seemed, was on a roll.   This was followed by The Progressive Era which went to the 1920s and The Roaring Twenties and The Great Depression.  Well we can have too much of a good thing. And like all good things, they eventually come to an end.  As to what caused the Great Depression, there are many theories. Certainly the market crash of 1929 was a major contributor. But the economy was already slowing with the dust bowl and people loosing their farms, a slow down in factory orders and consumption as well. I tend to go along with this theory.

Two economists of the 1920s, Waddill Catchings and William Trufant Foster, popularized a theory that influenced many policy makers, including Herbert Hoover, Henry A. Wallace, Paul Douglas, and Marriner Eccles. It held that the economy produced more than it consumed, because the consumers did not have enough income. Thus the unequal distribution of wealth throughout the 1920s caused the Great Depression.^[17][18]

According to this view, wages increased at a rate lower than productivity increases. Most of the benefit of the increased productivity went into profits, which went into the stock market bubble rather than into consumer purchases. Say's law no longer operated in this model (an idea picked up by Keynes).

As long as corporations had continued to expand their capital facilities (their factories, warehouses, heavy equipment, and other investments), the economy had flourished. Under pressure from the Coolidge administration and from business, the Federal Reserve Board kept the discount rate low, encouraging high (and excessive) investment. By the end of the 1920s, however, capital investments had created more plant space than could be profitably used, and factories were producing more than consumers could purchase.

According to this view, the root cause of the Great Depression was a global overinvestment in heavy industry capacity compared to wages and earnings from independent businesses, such as farms. The solution was the government must pump money into consumers' pockets. That is, it must redistribute purchasing power, maintain the industrial base, but re-inflate prices and wages to force as much of the inflationary increase in purchasing power into consumer spending. The economy was overbuilt, and new factories were not needed. Foster and Catchings recommended^[19] federal and state governments start large construction projects, a program followed by Hoover and Roosevelt.

As to what brought us out. Well that is also up for discussion even to this day.  But I would say that WWII was a big reason.  After all, at the end of WWII we were essentially the only game in town. Europe, Japan, England were all in ruins and the rest of the world had yet to really industrialize. Add to that we had all the oil we could steal from the Middle East and South America  plus defense spending on Korea and the Cold War.  Under those conditions it was very easy to have a great economy and people here did real well.  Wages were high and prices on most goods fairly low. American industry was doing great, unions were strong and unemployment low. 

But then Europe and Japan started rebuild and re-industrialize and their imports began  to show up. At first considered a joke and of poor quality, Japanese products were frowned upon. Junk was the term. German autos were either too expensive or looked too strange. But by the late 1960s these imports had made strong inroads to our economy. American business was for the first time having some real competition from abroad. On top of that, those countries in the Middle East where we had obtained our oil from, at rock bottom prices, started to overthrow our puppets that we installed and the price of oil went though the roof.

Taiwan and Korea and now China and India have entered the global market place. And a number of these countries still subsidize their industries. So their products were as well made as ours or even better and cost less as well.  Business here started to take a major hit as did our economy.

The prosperity of the post war years was actually a fleeting  period in our economic history. A fact that both those on the left and right refuse to consider. The yearning for the good old days of the past is simply an exercise in fantasy. That is unless you want to turn the rest of the world into rubble. Because to get to the conditions that allowed us that prosperity, that is what it would take.  Either that or a total reorganization of our business and financial institutions.