The Age of American isolationism was quickly replaced with the Age of American imperialism, which saw the expansion of the United States’ economic, political, and cultural influence beyond its borders during the final decades of the 19th century through the beginning of World War I. The annexation of Hawaii and the Spanish-American War occurred during this time, as did the building of the Panama Canal and exertion of U.S. control over places such as Cuba, Puerto Rico, Panama, and the Philippines.  Manifest Destiny was no longer a mantra that ended in California.  Westward expansion meant the islands of the Pacific to Asia, the Caribbean to Central America.   

When President McKinley was assassinated and Theodore Roosevelt took office in 1901, progressivism became a powerful national movement. During his tenure as president, Roosevelt was a loud and effective advocate for “trust-busting,” the breaking up of enormous monopolies that had controlled prices and prevented competition. He also advocated for fair trade and pro-labor laws, including a decreased workweek, child labor restrictions, and workplace safety rules.  Roosevelt, returning power to the White House not seen since Abraham Lincoln, set the stage for William H. Taft and Woodrow Wilson to continue the legacy of progressivism - that is, until World War I broke out.

Progressivism responded to the economic and social problems of a rapidly industrializing America at the turn of the 20th century. What began as a social movement, later grew into a political movement, largely out of its predecessor, the Populist movement. Progressives lived mainly in the cities, were college educated, and believed that government could be a tool for change. They concentrated on exposing the evils of corporate greed, combating fear of immigrants, and urging Americans to think hard about what democracy meant. It also gave a voice to an emerging African American civil rights movement. 

Inspired by the ideology of Manifest Destiny, which held that European Americans were divinely ordained to settle the whole of the North American continent, white settlers pushed ever further westward towards the Pacific. As they did so, they increasingly came into violent conflict with Native American Indians over land and natural resources, especially after the discovery of gold in western territories sparked the Gold Rush. Prospective gold-diggers flooded into the Rocky Mountains and Pacific Northwest, clashing—sometimes violently—with the Native Americans they encountered there. By 1890, the U.S. Census officially declared the frontier "closed."

Throughout the 1880s, local political action groups known as Farmers' Alliances grew rapidly among Middle Westerners and Southerners, who were discontented because of crop failures, falling prices, and poor marketing and debt. Although it won some significant regional victories, the alliances generally proved politically ineffective on a national scale - until the Populist Party of 1892. While trying to broaden their base to include labor and other groups, the Populists remained almost entirely agrarian-oriented. They demanded the unlimited coinage of silver, a graduated income tax, government ownership of the railroads, a tariff for revenue only, and the direct election of U.S. Senators.  And while their efforts did not win the White House, their legacy lasted into the 20th Century - through Progressives.

The Wild West, the American frontier, holds a special place in American history. Western films depict it as a place where the rules didn't apply, and where scores were settled with gun-slinging and shootouts. Early 20th Century Historian Frederick Jackson Turner argued that the frontier was not just a place, but a “process” that transformed people into the quintessential American. If settlers weren’t chasing gold, they were rounding-up cattle, or tilling open farmlands. Under the facade that Hollywood created, a life that was harsh and unforgiving.

Innovations of the Gilded Age helped usher in modern America. Urbanization and technological creativity led to many engineering advances such as bridges and canals, elevators and skyscrapers, trolley lines and subways.  But while the middle and upper classes enjoyed the allure of city life, little changed for the poor - particularly immigrants from Europe. Horrific living conditions, high crime rates and a pitiable existence lay below the gilded surface that was the American city.  This, amid rampant corruption in city politics and an era of forgotten U.S. Presidents.

In the mid-19th century, the vast majority of American work was still done on the farm. By the turn of the 20th century, the United States economy revolved around the factory.  The labor movement in the United States grew out of the need to protect the common interest of workers. For those in the industrial sector, organized labor unions fought for better wages, reasonable hours and safer working conditions. The labor movement led efforts to stop child labor, give health benefits and provide aid to workers who were injured or retired.

The late 19th Century was met with unprecedented levels of wealth. Railroads and soon, telephone lines, stretched across the country, creating new opportunities for entrepreneurs and cheaper goods for consumers. But a nation that had long viewed itself in idyllic terms, as a nation of small farmers and craftsmen, confronted the emergence of a society increasingly divided between the haves and the have-nots. Some Americans celebrated the new wealth, and others lamented it. All could agree that profound changes were taking place in the country.

Beginning in the early 1870s, railroad construction in the United States increased dramatically. Prior to 1871, approximately 45,000 miles of track had been laid. Between 1871 and 1900, another 170,000 miles were added to the nation's growing railroad system. Much of the growth can be attributed to the building of the transcontinental railroads.