Editor’s note: This is the 53rd in a series of essays on the history and meaning of the American political tradition.
The United States fought two wars of conquest during the 19th century. The first (1846-48), against Mexico, added new territories to the Southwest, which would later be incorporated into the United States. A half century later (1898), it fought the second war against Spain and acquired more new territories: Guam, The Philippines and Puerto Rico; it also became guardian of Cuba, which later became an independent nation, whose government the U.S. would unsuccessfully attempt to remove by force in 1961. The Philippines won international recognition as an independent nation in 1946, after a half-century of often-brutal colonial rule by the U.S., and for a brief interval, by Japan. Guam and Puerto Rico remain U.S. territories.
Two other territories were acquired beyond the continental boundaries of the 48 states. In 1894 the U.S. minister to the Kingdom of Hawaii conspired with American settlers there to overthrow the monarchy. They successfully carried off a coup d’état, deposed the monarch, Queen Lili’uokalani, and declared Hawaii an independent republic; in 1898, President William McKinley signed legislation annexing Hawaii as a U.S. territory. It became the 50th state in August 1959, following Alaska, which was admitted as the 49th state eight months before. Alaska, which had been a U.S. territory since 1867, was not acquired by conquest but by purchase, from imperial Russia. 
Two wars of conquest, a host of wars against the western Indian nations, a purchase from an imperial power, a coup, colonial rule, a civil war: in the light of all this, I am inclined to describe the second half of the 19th century as a period of imperial expansion. 
Strictly speaking, the United States is not an empire. The standard definition of an empire is a vast territory acquired by conquest and ruled by an absolute monarch. Only the first part of the definition fits — although the fantasies of our current chief of state suggest a trend toward completeness. 
Nevertheless, during the era from the Civil War to 1900, the Gilded Age, this nation underwent a surge of industrial and economic growth, carried out by entrepreneurs who operated without regulation to achieve their economic goals, monopolizing commodities, trade and production. This was the era of robber barons, so-called captains of industry: Cornelius Vanderbilt, John D. Rockefeller, Andrew Carnegie, to name a few. They exercised bare economic power ruthlessly and absolutely. They achieved their goals by degrading the natural environment and exploiting labor. It was a display of raw economic power; and they grew enormously rich by it. And there is no doubt this nation became a great power because of their actions, an empire without an absolute monarch, but led by businessmen whose wealth and financial genius made them absolute rulers of their domains. And by this means, this nation exercised dominion throughout the world. Unlike Rome, it did not require armies to extend its rule. It conquered by ruthless entrepreneurship. 
It is also worth remembering that this era of American imperialism coincided with the latter part of the Victorian Age, during which Britain encompassed the world. It was an era of triumph for English speaking peoples. 
Yet, during the same era, the nation underwent a great increase of population through emigration of peoples who were not English speaking; immigrants from Southern and Eastern Europe. To memorialize this, a Statue of Liberty was erected in New York Harbor, a gift “from the people of France to the people of the United States.” It bears this inscription taken from a poem by Emma Lazarus, written in 1883, entitled “The New Colossus,” which I quote in full:
Not like the brazen giant of Greek fame,
With conquering limbs astride from land to land;
Here at our sea-washed, sunset gates shall stand
A mighty woman with a torch, whose flame
Is the imprisoned lightning, and her name
Mother of Exiles. From her beacon-hand
Glows world-wide welcome; her mild eyes command
The air-bridged harbor that twin cities frame.
“Keep, ancient lands, your storied pomp!” cries she
With silent lips. “Give me your tired, your poor,
Your huddled masses yearning to breathe free,
The wretched refuse of your teeming shore.
Send these, the homeless, tempest-tost to me,
I lift my lamp beside the golden door!”
Only the last four lines, here printed in italics, appear in the inscription. Lazarus wrote the poem as part of a fundraising effort to pay for the pedestal of the statue.
A colossus is a sculpted figure larger than life, which is supposed to represent the imagined political power of a nation. The “Greek colossus” to which Lazarus referred, otherwise known as the Colossus of Rhodes, was created as a monument to military might. Lazarus imagined the American colossus to represent something very different. Her colossus is a woman, a “Mother of Exiles,” who welcomes the persecuted masses, Europe’s “wretched refuse.” At the same time, she looks with scorn towards the imperial pomp of old Europe. 
“Empire of Liberty” is the title of a book written by the American historian Gordon Wood. The volume deals only with the founding of the nation, but its title might even better describe what the United States, guided by its better angels, was striving to become during this period: a welcoming place, where people throughout the world seeking safety might find refuge, a nation of immigrants, no longer purely white, Anglo-Saxon and Protestant, but polyglot and multicultural. This was Emma Lazarus’s vision of America. And if the vision had become a reality, the empire of United States would be a very different empire from any that the world has ever seen. And perhaps it is to some extent, to the extent as it has opened its borders to peoples needing a place where they may be safe, a sanctuary, and the opportunity to live a good life.
But Emma Lazarus was a victim of anti-Semitism. Indeed, during the late 19th and early 20th centuries, reaction to the flood of emigrants found expression in ever new vile prejudices: against Catholics, Eastern and Southern Europeans, Asians and more. These hateful prejudices coalesced with the American original sin of racism. And, if one were to fast-forward to the present, we should add Islamophobia, and prejudice against Hispanics. “Empire of Liberty” is a fitting expression, only if it is said ironically.