1

Louisiana Purchase (1803)

Image: Nik Shuliahin

It sounds crazy today, but the Louisiana Purchase almost doubled the size of the United States overnight. Thomas Jefferson, at the time, the third to occupy the position of President of the United States, bought the massive 828,000 sq mi territory from France for $15 million, securing vital land and resources.

The purchase, however, didn’t mean that the United States also gained control of the totality of the territory, as it was inhabited by Native Americans. But in any case, the acquisition paved the way for westward expansion, providing a vast area for exploration and settlement, while enhancing America's geopolitical influence.

2

Lewis and Clark Expedition (1804-1806)

Image: Charles Marion Russell

Commissioned by Jefferson, Meriwether Lewis and William Clark then embarked on a mission to map the newly acquired lands and find a viable route to the Pacific. Their legendary journey revealed the rich diversity of the western territories and established crucial relationships with Native American tribes.

Sacagawea, a Shoshone woman, played a crucial role as an interpreter and guide, helping the expedition navigate difficult terrain and gain trust with native tribes, significantly contributing to the mission's success. Ultimately, their detailed reports opened the frontier to future explorers and settlers.

3

The Oregon Trail (1811-1869)

Image: Dana Davis

Originally laid around 1811 by fur trappers and traders, the Oregon Trail soon became a critical route for thousands of emigrants moving west. Spanning over 2,000 miles from Missouri to Oregon, it was a perilous journey marked by harsh landscapes and, more often than not, disease.

Despite the hardships, the trail was improved to become passable by wagons, and it facilitated the mass migration of over 400,000 settlers during its peak, significantly contributing to the population growth and development of the Western United States.

4

California Gold Rush (1848-1855)

Image: Viviana Rishe

The discovery of gold at Sutter's Mill in 1848 triggered a massive influx of fortune seekers to California. The Gold Rush not only boosted the economy but also accelerated California's admission claim as the 31st state in 1850.

While prospectors initially used simple techniques like panning, the increasing complexity of gold extraction eventually required significant financing, favoring mining companies. And though the gold rush generated wealth worth tens of billions in today's dollars, only a few became rich; most participants earned little more than they had started with.

5

Homestead Act (1862)

Image: Kevin Butz

Signed by President Abraham Lincoln, the Homestead Act offered 160 acres of public land to settlers willing to farm it for five years. The policy primarily encouraged individual farmers who were looking to operate their own farms, as opposed to slave owners who sought to buy large tracts of land and use slave labor.

The legislation encouraged widespread migration to the Great Plains, accelerating agricultural development and expanding American settlements across the West.

6

Building of the Transcontinental Railroad (1863-1869)

Image: Johannes Plenio

The completion of the first Transcontinental Railroad in 1869 revolutionized transportation in the United States. Connecting the East and West coasts, it facilitated trade, travel, and communication.

The extensive railroad network was built by three private companies on public lands, financed with federal bonds and various subsidies. Instrumental in the nation's economic growth, the Transcontinental Railroad also helped forge a sense of national unity and identity in the American consciousness.

7

The Great Sioux War (1876-1877)

Image: Popular Graphic Arts

Also known as the Black Hills War, the Great Sioux War was a series of conflicts between the United States and the Sioux tribes. The war was sparked by the encroachment of settlers and gold prospectors on Native lands, a conflict that had been escalating since the early 19th century.

Despite many Native American victories, such as the Battle of Little Bighorn - better known as Custer's Last Stand -, the war ultimately ended in the tribes' displacement. The conflict officially finished with the Agreement of 1877, in which the Sioux tribes were forced to cede property rights of their lands to the federal government, while clearly demarcated Indian reservations were established.

8

Oklahoma Land Rush (1889)

Image: Raychel Sanner

On April 22, 1889 - soon after the signing into law of the Indian Appropriations Act, which freed over two million acres of land for settlement - thousands of settlers raced to claim land in the Oklahoma Territory during the first of several land rushes.

Those who followed the rules and waited for the official start of the land rush were known as "boomers," while "sooners" sneaked into the territory before the designated time, risking penalties but gaining advantageous claims. This sparked hundreds of legal contests that had to be settled at local land offices or even by the U.S. Department of the Interior.

9

The Dawes Act (1887)

Image: Boston Public Library

The Dawes Act aimed to assimilate Native Americans by dividing tribal lands into individual allotments. While intended to promote agriculture and integration, it resulted in the loss of tribal lands and culture.

The act was a controversial effort to reshape Native American society in the image of European-American settlers. It wasn’t until the Indian Reorganization Act, passed during the Franklin D. Roosevelt administration, that Native Americans regained some of their rights to own land collectively and form self-government.

10

Closing of the Frontier (1890)

Image: Aaron Burden

In 1890, the U.S. Census Bureau declared the frontier closed, as there was no longer a discernible frontier line. This marked the end of a significant era of American expansion.

The closing of the frontier signified the nation's transition from a period of exploration and settlement to one of modernization and industrialization.

1

Raven Rock Mountain Complex

Image: Ilagam

Did you know that in the 1950s, the US government carved out a secret underground city that could survive a nuclear attack? It’s called an "underground Pentagon", and very much like Area 51, it is one of the government's most classified projects.

This military complex and nuclear bunker is located near Blue Ridge Summit, Pennsylvania, 768 feet below the ground. It’s protected by 23.5 ft thick 30-ton doors built on top of springs to survive the shock from a blast. Raven Rock has five buildings with 15 floors big enough to live and work. The base has everything it needs to keep running, like a cafeteria, a barbershop, water generators, and even a medical center.

2

SubTropolis

Image: mwewering

Below Kansas City, Missouri, lies the world's largest underground business complex. SubTropolis is a structure located inside a mine north of the Missouri River. It was carved out of limestone some 135 to 185 feet underground and covers a total of 55 million square feet.

Kansas City Chiefs founder Lamar Hunt built this subterranean city in the 1960s. It has offices, storage space, and even factories. Over 1,600 people work here every day, largely because SubTropolis remains cool all year, making it an ideal location for businesses. Fun fact: some of Hollywood’s most beloved masterpieces are kept here, including the original film reels of Gone with the Wind and The Wizard of Oz.

3

Underground Atlanta

Image: Ronny Sison

Underground Atlanta is a historic spot in downtown Atlanta, Georgia. It was built in the late 1800s, right after the Civil War, as a commercial district centered around the railroad. In the 1920s, viaducts were built and the streets were raised, creating a second level of streets, buildings, and shops.

During Prohibition, the abandoned underground space served as the best spot for speakeasies and juke joints. For decades, people forgot about the hidden city, but in the 1960s, it was brought back to life as a fun place for music bars and nightlife.

4

New York City Subterranean World

Image: Photographer: unknown, Public domain, via Wikimedia Commons

Under America’s most populous city, there's a whole hidden world. For example, beneath Little Italy and the Public Library, there are secret vaults. Beyond the subway millions of people use daily, there is City Hall station, opened in 1904 and closed in 1945. It's a hidden gem with stained glass and mosaics that you can still visit by staying on the 6 train past the last stop.

But that’s not all! There are trading tunnels in SoHo and old cattle tunnels in the Meatpacking District. Also, in 1897, there were mail tubes built around the city to send letters between post offices that operated until the 1950s. Some of these underground spaces go as deep as 800 feet!

5

Permafrost Tunnel Research Facility

Image: Paxson Woelber

A large part of the land in the northern hemisphere is Permafrost, so it makes sense that there is a research facility specially built to study it. The Permafrost Tunnel in Alaska is the best place to learn about frozen soil that's over 40,000 years old.

The long tunnel was dug from 1963 to 1969 to study how to build and mine in frozen environments. Inside the facility, scientists study ice, ancient plants, and even bones from animals like mammoths. The tunnel shows different layers of earth, uncovering frozen ground from different time periods that help scientists anticipate what might happen as the world gets warmer.

6

The Greenbrier Bunker

Image: Alex Holzreiter

The Greenbrier Bunker in White Sulphur Springs, West Virginia, is a secret underground facility beneath a luxury hotel that has hosted numerous US presidents and famous guests. It was built during the Cold War to protect the US Congress in the event of a nuclear attack. The bunker was designed to house all 535 members of Congress and their staff for a long time.

This classified underground facility remained a secret until 1992, when a Washington Post article exposed it. Today, visitors can take tours to see special rooms, blast doors, and decontamination areas.

7

The Caverns

Image: jymy duhomme

Would you attend a concert underground? If you travel to Tennessee is totally possible! The Caverns, formerly known as Bluegrass Underground, is a very cool spot in Grundy County, Tennessee. Lying deep in a cave 333 feet underground, this concert venue with natural acoustics is the perfect place for live music.

People come from all over to hear a variety of performances, especially Bluegrass music. The Caverns can accommodate up to 1,200 people standing up and are equipped with state-of-the-art sound and lights. The cave's cool and quiet atmosphere makes the experience extra special!

8

Crystal City Underground

Image: Gustavo Alejandro Espinosa Reyes

Beneath the neighborhood of Crystal City, near Washington, DC, lies a network of shops, restaurants, and offices. It opened in 1976 and was designed to feel like an old shopping village with cobblestone streets and antique glass windows.

The underground space covers 150,000 square feet and connects several buildings. It's a popular spot for office workers and visitors, especially when the weather is bad. Unfortunately, in 2024, the shops closed, ending their retail era. Yet, the underground walkways and connections to the Metro remain open for pedestrians.

9

Los Angeles Prohibition Tunnels

Image: Alpha Perspective

In the 1920s, during Prohibition, people had to find ingenious ways around the restrictions on selling and consuming alcohol. That's why they built about 11 miles of underground tunnels right under Los Angeles.

Many of these subterranean sites are now closed, but you can still find a few hidden entrances around the city. You can even go on a tour to explore the tunnels and learn about their secret history.

10

Havre Beneath the Streets

Image: Đào Việt Hoàng

After a big fire in 1904 destroyed Havre’s business district in Montana, many shops moved underground. They used the old steam tunnels to stay safe from fires and bad weather. For years, the tunnels were busy with people and stores, such as saloons, drugstores, laundromats, and even a brothel. But today it is completely silent.

Fortunately, you can still visit what is left of this hidden city to see old shops and learn how people stayed safe and worked over 100 years ago. It's like going back in time!

11

Cheyenne Mountain Complex

Image: See page for author, Public domain, via Wikimedia Commons

One of the safest places in the world is right here in America, more specifically in El Paso County, Colorado. Hidden inside a mountain, Cheyenne Mountain Complex was built in the 1960s to protect the US military from nuclear attacks.

The bunker stands under 2,000 feet of solid Granite, making it super strong and safe. It was once the command center for NORAD (North American Aerospace Defense Command). The complex has blast doors that weigh 25 tons each and can withstand a nuclear blast. It also has its own power, water, and food supply. People could survive there for months!

12

Forestiere Underground Gardens

Image: Levi Clancy, CC0, via Wikimedia Commons

A Sicilian immigrant called Baldassare Forestiere spent 40 years digging and building a series of subterranean structures by hand in Fresno, California. Inspired by Roman catacombs and old wine cellars, he created around 65 rooms, tunnels, and courtyards to escape the hot summer sun.

The Gardens have fruit trees, grapevines, fishponds, and even a chapel. Some of the trees are more than 90 years old! Today, Forestiere Underground Gardens is a Historical Landmark you can visit if you want to discover a true underground paradise.

1

The disappearance of Amelia Earhart (1937)

The first entry on our list is dedicated to a world-renowned flight pioneer, Amelia Earhart, who vanished while attempting to become the first woman to fly around the globe , leaving behind only fragments of her plane and endless speculation. Radio failure, poor visibility, and fuel issues are speculated to be contributing factors to her disappearance.

Even with modern technology and repeated searches, no one has ever found definitive proof of what happened to Amelia or her aircraft.

2

The D.B. Cooper hijacking (1971)

In 1971, Dan Cooper, a seemingly quiet man, boarded a plane in Portland, Oregon, which he promptly hijacked when the aircraft was in the air. He demanded $200,000 over the radio.

The plane landed in Seattle, where authorities met his demands. Cooper released all 36 passengers in exchange for the cash and parachutes. He then ordered the remaining crew to fly toward Mexico City at a low altitude and slow speed. Somewhere over southwest Washington, he lowered the aircraft's aft stairs and jumped into the freezing night, never to be seen again.

3

The disappearance of Jimmy Hoffa (1975)

The powerful union leader left a Detroit restaurant in 1975 and simply vanished . Witnesses last saw him standing by his car in the restaurant’s parking lot, and investigators believe he was coaxed into a car by people he recognized, thinking the meeting location had changed. He was never seen again. Searches in fields, lakes, and construction sites turned up nothing. To this day, it remains one of the most famous unsolved mysteries in American history.

Rumors range from mob connections to government cover-ups, but none have been proven. Ever since then, Hoffa’s name has become shorthand for anything that disappears without a trace.

4

The Yuba County Five (1978)

In what came to be known as "America’s Dyatlov Pass", five friends vanished after attending a basketball game in the town of Chico, California. Months later, the bodies of four members of the group were found in the mountains under mysterious conditions .

The remaining member of the original party was never located, and their strange route into deep snow remains unexplained.

5

The Sodder Children (1975)

A fire destroyed the Sodder family home in West Virginia, but five children were never found among the remains of the house. Because of physical inconsistencies at the scene and strange sightings afterward, the family always believed they survived.

Over the years, strange sightings and letters fueled hope and confusion alike, but no real evidence has ever been found. Because of these clues, the Sodders never held a funeral and instead famously erected a billboard on Route 16, offering a reward for information and keeping the case in the public eye for decades.

6

The Springfield Three (1992)

On a warm summer night in 1992, Sherrill Sherrill Levitt, her daughter Suzie, and Suzie's friend Stacy vanished from their home in Springfield, Missouri, leaving behind their cars, purses, and even the family dog .

Friends arriving the next morning found the house empty but unlocked. Despite thousands of leads, no evidence or remains have surfaced. The case remains one of the most talked-about disappearances in small-town America to this day.

7

The Gardner Museum Heist (1990)

Back in 1990, two men dressed as police officers entered Boston’s Isabella Stewart Gardner Museum and stole 13 works of art worth over $500 million .

No piece has ever been recovered. Empty frames still hang on the museum walls, a quiet tribute to one of history’s most expensive thefts.

8

The Max Headroom broadcast hijack (1987)

1980s television viewers might remember Max Headroom as a somewhat clumsy computer AI TV personality and ad spokesperson. In 1987, Chicago viewers were startled when a strange figure wearing a Max Headroom mask interrupted TV broadcasts with odd messages .

The stunt lasted only seconds, but no one was ever caught or identified. It remains one of the strangest unsolved moments in television history.

9

The Great Lakes ghost ships

Over the years, s everal ships have vanished or been found adrift on the Great Lakes , their crews gone without explanation. Cold weather, sudden storms, and superstition all play roles in the stories, but some cases defy logic. The vast inland seas are simply too big to be accessible with the current technology.

Among the most notable unsolved cases, we can mention Le Griffon, a ship that vanished during her maiden voyage in 1679, the SS Banockburn, known as the "Flying Dutchman of Lake Superior," disappeared during a storm in 1902, or the SS Chicora, a luxury steamer lost in a violent winter gale while carrying a cargo of flour, in 1895.

10

The Dulce Base Mystery

Beginning in the 1970s, a constant array of strange lights, unmarked aircraft, and talk of secret tunnels near the town of Dulce has fueled decades of conspiracy theories in this otherwise quiet area to this day.

While skeptics blame radar tests or imagination, locals still report odd sightings in the desert skies.