The United States entered the 20th century in a state of flux. The world was changing, the nation was changing, and it was about to change even more. The changes in the country—and in the world—since 1800 were by far the most dramatic of any century since ancient times. Communication devices such as the telegraph and telephone; transportation means such as railroads, streetcars and automobiles; ready made clothes and canned foods; electric lighting; indoor plumbing; and myriad other technological wonders were all but unimaginable to Americans in 1800. The population of the United States increased from approximately 5 million to over 75 million people, and the ethnic makeup of the country had shifted, beginning with the great flood of Irish immigrants before the Civil War and continuing thereafter, when more and more immigrants from eastern and southeastern Europe arrived on America's shores.

The industrial revolution, which actually began during the Civil War, began to accelerate rapidly once the conflict was over. Railroads had been a vital element in the Union victory over the Confederacy, and railroad builders immediately set out completing the project which had been envisioned before the Civil War, namely, the construction of the first continental railroad, completed in 1869 in Promontory, Utah. Three more transcontinental lines, the Southern Pacific, Northern Pacific, and Atchison, Topeka and Santa Fe. Each of those major trunk lines spurred the building of many other smaller lines connecting important cities to the transcontinental network.

While those railroads, steel plants, electrical works, automobile factories and other modern inventions created thousands of jobs and great wealth for many, the working conditions of the laborers were often horrendous. Reformers and labor unions agitated for change, but during the Gilded Age, reform was slow in coming. Many people around the turn of the century felt that the enormous progress recently experienced was about to level off; indeed, the Director of the United States patent office around 1900 declared that within a decade or so his office would close, since everything conceivable had already been invented. Even as the Wright brothers were planning their first heavier-than-air flying machine, scientists were beginning to investigate the powers of radiation and the mysteries of the atom. Not only would the rate of change not level off; it would continue to accelerate throughout the 20th century and beyond.

This part of the site will focus on the great age of reform: the Progressive Era. The spirit of reform has been an element of the American character for most of the nation's history. The entire American revolutionary experience was in a sense about reform, as the government that was created by the founding fathers opened up a new era of republicanism, moving inexorably towards greater democracy. The antebellum period saw advances in prison reform, the temperance movement confronted alcoholism, and the first steps were taken towards improving the lots of women in America's political society. As America entered the industrial age between the Civil War and 1900, however, new challenges faced the American people.

Technological change brought great benefits to masses of people; at the same time, it made life infinitely more painful for those in the lower echelons of society. The great economic gains of the 19th century left many Americans in deplorable conditions, as we saw in the chapter on the Gilded Age. By 1900 many could sense a smoldering sense of rebellion that went beyond the protests of the Populist movement. Things were going to change, one way or another, and the Progressive Movement aided in making those changes more constructive than destructive, although the so-called war between capital and labor did not disappear altogether.

Where the focus of the last chapter tended to be on the poor, the downtrodden, and the exploited, this period will see us focused on the changing role of government, both domestically and internationally. From being an almost passive observer of the development of the nation, the government became an active player in facilitating change, generally for the better. The term progressive has always been associated with the political left, and it began with the Progressive Era. Although the most famous Progressive era politician, Theodore Roosevelt, has never been called liberal, his political opponents, mostly in his own Republican Party, were the conservatives. His 1913 Autobiography underscores that point.

During the same era, in the following section we will see the United States transformed from a sideline observer in the international world to a major participant in the great events of the 20th century. Whether the latter development was for good or ill is still being debated.