The Compromise of 1850 tried to settle disputes over land gained from Mexico

The Treaty of Guadalupe Hidalgo forced Mexico to surrender over half its territory

Signed in 1848, the Treaty of Guadalupe Hidalgo ended the war but came at a steep cost for Mexico—ceding 55% of its territory, including California and the Southwest, in exchange for $15 million and vague promises to protect Mexican residents.

US westward expansion—and the status of slavery in the new territories—was a major cause of the American Civil War

The addition of new western lands forced the nation to confront whether slavery would spread beyond the South. Each debate over the admission of a new state sharpened the divide between free and slaveholding regions.

The Missouri Compromise temporarily eased tensions over slavery's expansion

Passed in 1820, the Missouri Compromise admitted Missouri as a slave state and Maine as a free state—maintaining the fragile balance between proslavery and antislavery states in Congress. It also banned slavery north of latitude 36°30′.

How the US took half of Mexico

In just two years, the United States redrew the map of North America. Sparked by border disputes in Texas and fueled by President James Polk’s drive for expansion, the Mexican–American War (1846–1848) reshaped both nations.

Learn how Mexico’s anti-slavery stance shaped the US–Texas conflict

Historian Alice Baumgartner explores how Mexico’s abolition of slavery clashed with Anglo settlers' ambitions in Texas. The episode reveals how enslaved people fled south to freedom, reshaping the politics that led to Texas independence and the Mexican-American War.

American annexation of Texas eventually sparked war with Mexico

After Texas won independence from Mexico in 1836, the US annexed it in 1845—despite Mexico’s refusal to recognize Texas as separate. That annexation, combined with a heated border dispute, triggered the Mexican-American War the following year.

The Kansas-Nebraska Act sparked violence that foreshadowed the Civil War

The 1854 Kansas-Nebraska Act let settlers vote on whether to allow slavery, repealing the Missouri Compromise. Competing proslavery and antislavery groups poured into Kansas, sparking years of bloody conflict known as "Bleeding Kansas."

President Polk deliberately provoked war with Mexico

After Mexico refused to sell California and New Mexico, President James K. Polk ordered US troops into disputed territory between the Nueces River and the Rio Grande—knowing it would likely spark a conflict. When fighting broke out, he used it to justify declaring war.

Mexico admired Lincoln for opposing the war and supporting Mexican sovereignty

As a congressman, Abraham Lincoln condemned the Mexican-American War as unjust. Years later, as president, he backed Mexico’s fight against French occupation. His principled stance earned enduring respect and monuments across Mexico.

The Lincoln-Douglas debates sharpened the national divide over slavery

In 1858, Abraham Lincoln and Senator Stephen Douglas debated while competing for an Illinois Senate seat. Their seven debates, reprinted nationwide, brought the question of slavery to the forefront—further polarizing the country and propelling Lincoln to national prominence.

Mexico’s political chaos weakened its defense against US invasion

Mexico’s post-independence instability—marked by coups, power struggles, and weak central control—left its northern frontier vulnerable. That political fragmentation shaped Mexico’s unpreparedness during the Mexican-American War and helped enable US conquest.

US troops committed widespread atrocities during the Mexican-American War

American volunteer regiments frequently looted towns, raped civilians, and executed prisoners—especially in occupied northern Mexico. Historians have documented how racial hatred and impunity fueled war crimes that were rarely punished by military leadership.

The Constitution included compromises that still shape the US today

The creation of the Constitution necessitated numerous compromises to accommodate the diverse interests of the states. The significant compromises included resolutions on debates over representation in Congress and the status of enslaved individuals.

Cinco de Mayo holiday celebrations originated with California's Mexican Americans during the Civil War

California Latinos first celebrated Cinco de Mayo in 1862 through patriotic assemblies called Juntas Patrióticas. Ardent Union supporters, these individuals saw the Puebla victory as a win for democracy against both French imperialism and the Confederate cause.

France, Spain, and Britain formed a joint military alliance to force Mexico to repay its debts

In October 1861, the three powers signed the Convention of London and landed troops at Veracruz that December. Britain and Spain reached settlements with Mexico and withdrew. France refused and aimed to change the regime in power in Mexico.

Congress's Wade-Davis Bill demanded harsher terms for Southern reentry

Passed in 1864, the Wade-Davis Bill required 50% of white male voters to swear loyalty and guarantee emancipation before readmission. Lincoln pocket-vetoed it, rejecting Congress's stricter approach.

Madison urged Jefferson to accept the Louisiana Purchase despite constitutional concerns

As secretary of state, James Madison helped negotiate the 1803 Louisiana Purchase and persuaded Thomas Jefferson to proceed, arguing that the strategic and economic stakes outweighed the unresolved constitutional questions.

The disputed 1876 Presidential election accelerated the end of Reconstruction

The 1876 election between Rutherford B. Hayes and Samuel J. Tilden ended in a deadlock over contested Southern votes. To resolve the crisis, Democrats accepted Hayes's presidency in exchange for the withdrawal of federal troops—formally ending Reconstruction.

Ranchos were large land grants in California to Spanish, Mexican leading families

They were typically given to leading families or retired soldiers as means of settling the land with loyal people. The hundreds of ranchos have since shaped land-use policy in the area, determining plots of major cities and ranches today.

The nullification crisis tested whether states could defy federal law

In the 1830s, South Carolina declared federal tariffs void within its borders. President Andrew Jackson threatened military force, Congress passed a compromise tariff, and the episode ended with federal authority prevailing over state nullification.

The Dawes Act of 1887 broke up communally held tribal lands

Sometimes called the General Allotment Act, the Dawes Act divided reservation land into individual plots assigned to Native Americans, while "surplus" land was sold to white settlers. The policy led to Native tribes losing roughly 90 million acres, about two-thirds of their remaining land.

Opposing policies over immigration and sanctuary cities define the contemporary debate over federalism

Disputes between the federal government, Republican-controlled states, and Democratic-controlled cities over immigration enforcement and sanctuary policies have become a central flash point in modern federalism. These conflicts will shape the future of state autonomy, federal authority, and the enforcement of national policy across jurisdictions.

The Monroe Doctrine promoted 4 core principles

Monroe outlined four positions: the US would not interfere in European conflicts; it would not disturb existing European colonies in the Americas; the Western Hemisphere was closed to new colonization; and any European attempt to control an independent American republic would be regarded as a threat to US security.

In 2025, Democratic-led states moved to counter with their own redistricting plans

In response to Republican mid-decade redistricting efforts, Democratic leaders in California, New York, Illinois, and Maryland signaled plans to revisit their own congressional maps.

Catalonia and the War of the Spanish Succession

The War of Spanish Succession (1702-1715) was an international and civil war that reshaped Europe’s political landscape and brought Catalonia under Spanish rule. Created by the Museum of the History of Catalonia in Barcelona, this virtual exhibit guides readers through the 13-year war with a specific eye for its effects on Catalonia. Galleries of artwork from the period on the right-hand side of the page help immerse visitors in the history.

The rivalry between Alexander Hamilton and Thomas Jefferson centered on federalism—the question of how much power the federal government should hold relative to the states.

Abraham Lincoln was almost assassinated weeks before his inauguration as he traveled from Illinois to DC through Baltimore in 1861; it took two independent claims for Lincoln to be convinced the threat was real

The United States has had a tumultuous relationship with Cuba since its 1959 revolution, highlighted by a nuclear crisis and a decades-long trade embargo.

Mark Twain spent decades feuding with the US Postal Service, convinced its costs and regulations were bureaucratic overreach.

Explore an interactive map of battles from the American Revolution, along with detailed summaries of each engagement

70 years ago today, city officials in Santa Cruz, California, banned rock 'n' roll to protect its youth from corruption after witnessing a 'provocative' concert the night before.

Despite being favored by 87% of Americans, Congress does not have term limits.

See a 3D reconstruction of Tenochtitlan, the Aztec capital that was home to an estimated population of 200,000 to 400,000.

'Grand Canyon of the Yellowstone,' a work by American painter Thomas Moran, inspired Congress to establish Yellowstone National Park.

Gerrymandering works through two techniques: cracking opposing voters across districts to dilute their power, and packing them into a few to waste their votes in lopsided majorities.

The use of fungi to detoxify land and water—a process known as mycoremediation—has been used to clean up natural resources affected by the 2025 California wildfires.

The story of Dollree Mapp, whose legal challenge over her 1957 conviction for possessing "obscene material" led to a major strengthening of the Fourth Amendment

Before writing 'Walden,' transcendentalist Henry David Thoreau nearly burned down his hometown with a campfire that grew out of control.

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

See this overview of the firework rules across all 50 states, ranging from a complete ban on non-professional fireworks in Massachusetts to states with more lax rules like Indiana.

20,000 letters to the advice columnist 'Dear Abby' provide insight into prevailing sex, religion, and LGBTQ fears, anxieties, and concerns from the 1950s onward.

Domino's Pizza's 30-minute delivery guarantee was responsible for the chain's 1980s surge, but it was discontinued after the company was found liable for delivery driver accidents.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

The Brothers Grimm were lawyers before they were storytellers, but became interested in fairy tales as they began investigating how rules and customs had been passed down through cultures.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

Play the role of a student in a game where you try to navigate college and remain debt-free, selecting different income levels, high school experience, race, ethnicity, and more.

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

SpaceX's S-1 or 'prospectus' revealed many previously unknown details about the company, including its unprofitability despite doing $18.7B in revenue in 2025, exactly how many voting shares Elon Musk will have in the company (roughly 85%), and more.

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.