Future President Abraham Lincoln challenged Polk’s justification for war with Mexico

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.

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.

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.

The Prize Cases established that the president can respond to an attack without waiting for Congress to act

When Lincoln blockaded Confederate ports at the start of the Civil War without congressional authorization, the Supreme Court upheld his actions, ruling that a president does not initiate war by responding to an attack and need not wait for Congress when the nation is already under threat.

Manifest destiny fueled US aggression against Mexico

The belief that the United States had a divine right to expand westward—known as manifest destiny—justified President Polk’s push for territorial conquest. It shaped public support for the Mexican-American War and framed the invasion as national destiny.

In the midst of the Civil War, Lincoln rapidly expanded presidential power

Abraham Lincoln suspended habeas corpus, expanded the army without congressional approval, and issued the Emancipation Proclamation—despite likely lacking authority to unilaterally alter national slave law. His actions set precedents for expanded presidential power in wartime.

Abraham Lincoln received only 40% of the popular vote in the 1860 election, highlighting the deep divisions in the country on the eve of the Civil War.

Abraham Lincoln's victory in 1860 sparked Southern secession—even before his inauguration

Abraham Lincoln's election on an antislavery expansion platform convinced many Southerners that their way of life was under threat. Within three months, seven states seceded from the Union—forming the Confederacy—before Lincoln took office in March 1861.

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

Territory acquired in the Mexican-American War reignited fierce debates over slavery’s expansion. The Compromise of 1850 aimed to ease tensions by admitting California as a free state and letting other territories decide the issue—but the compromise ultimately failed and helped pave the way to the Civil War.

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.

Foreign policy and war defined Madison's presidency

During James Madison's presidency, disputes with Britain and France over trade, maritime rights, and impressment dominated foreign policy, culminating in the War of 1812 and shaping how the United States engaged with major European powers.

Truth met President Lincoln at the White House in 1864

In October 1864, Truth traveled to Washington and met President Lincoln a week before his reelection, though she could secure the appointment only through a white abolitionist friend. Lincoln signed her autograph book, and Truth later said she had never been treated with more "kindness and cordiality" by anyone.

A detective foiled an assassination plot against Lincoln before his inauguration

In February 1861, detective Allan Pinkerton uncovered a plot to kill Abraham Lincoln en route to his inauguration. Lincoln secretly altered his travel plans and sneaked into Washington DC to take the oath of office. Pinkerton later founded the well-known Pinkerton's National Detective Agency.

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.

Lincoln's original reconstruction vision prioritized reconciliation

Proposed in 1863, Lincoln's Ten Percent Plan offered lenient readmission for Southern states once 10% of voters pledged loyalty and ended slavery. It was adopted in a few Union-occupied areas but was only partially implemented before his assassination in 1865.

Madison was America's first president during a formally declared war

During James Madison's presidency, Congress formally declared war on Britain in 1812 over its practice of seizing American sailors, trade restrictions, and repeated violations of US sovereignty—marking the first time a sitting American president led the nation through a declared war.

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.

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."

Zachary Taylor became a national hero during the Mexican-American War

General Zachary Taylor led US forces to key victories in northern Mexico, earning widespread fame for his leadership. His popularity from the war propelled him to the presidency in 1848.

The Mexican-American War trained future Civil War generals

Many key military leaders of the Civil War—including Ulysses S. Grant, Robert E. Lee, and Thomas “Stonewall” Jackson—first saw combat in the Mexican-American War, gaining battlefield experience that shaped their later commands.

Whitman led a Lincoln lecture late in life

Whitman toured several cities with “The Death of Lincoln,” a lecture series about the slain president that sought to establish him as a crucial figured in American history. The talks attracted famous figures, including Mark Twain and General William Tecumseh Sherman.

In his 1859 annual message to Congress, President Buchanan articulated a narrow view of presidential military authority

Buchanan argued that the president lacked constitutional authority to launch offensive military action without congressional approval, a view that reflected the prevailing interpretation of executive war powers throughout much of the nineteenth century.

Former American President Abraham Lincoln is one of history’s most famous ghosts

Abraham Lincoln, Anne Boleyn, Pausanias, and the Maharajah Duleep Singh are just a few of the notable phantoms found around the world. Several White House occupants and visitors have claimed to see Lincoln, including Theodore Roosevelt, Grace Coolidge, and Winston Churchill.

James Monroe first outlined what became known as the 'Monroe Doctrine' during his 1823 Annual Message to Congress

President Monroe used his Annual Message to Congress to warn European powers against further colonization in the Western Hemisphere, asserting US opposition to foreign intervention and laying the foundation for a cornerstone of American foreign policy that remains to this day.

Thoreau's 'Civil Disobedience' was largely a protest against the Mexican-American War

Henry David Thoreau refused to pay taxes that funded what he saw as an unjust war waged to expand slavery. His act of protest inspired his famous essay "Civil Disobedience," a foundational text for nonviolent resistance.

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 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.

Lincoln's Gettysburg Address became one of the most famous speeches in American history

Delivered by Lincoln on Nov. 19, 1863, at the dedication of a national cemetery, the 272-word Gettysburg Address reframed the war as a struggle for equality. The speech would be cited as a moral touchstone for later movements such as women's suffrage and civil rights.

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.

The first test of America's war powers came just a decade after the Constitution was ratified

During the undeclared Quasi-War with France in 1800, the Supreme Court ruled in Bas v. Tingy that Congress had authorized a valid "imperfect war" through statutes alone, without a formal declaration, establishing that there is a legal spectrum between peace and declared war.

Read an excerpt from the Monroe Doctrine, introduced in Monroe's 1823 address to Congress

On Dec. 2, 1823, President Monroe delivered his seventh annual message to Congress, now known as the State of the Union. One segment—warning European powers against interfering in the Western Hemisphere—became known as the Monroe Doctrine.

The Lincoln Memorial was almost never built

The Memorial faced years of opposition from Speaker of the House Joseph Gurney Cannon, who blocked it for nearly a decade, arguing that the swampy land west of the Mall was an unfit and undignified site to honor Lincoln.

Support for slavery helped drive Texas to revolt against Mexico

Mexico abolished slavery in 1829, but many Anglo-American settlers in Texas brought enslaved people and refused to comply. Their desire to preserve slavery was a major factor in Texas’s 1836 rebellion and independence from Mexico.

Lincoln was assassinated by a well-known actor, who originally planned to kidnap him

On April 14, 1865, actor John Wilkes Booth shot President Abraham Lincoln at Ford's Theatre in Washington, DC. Booth had initially conspired to kidnap Lincoln but turned to assassination after the Confederacy's defeat.

Presidents from both parties have resisted the authority of the War Powers Act

Presidents from both parties have treated the War Powers Resolution as voluntary, framing compliance as seeking "support" rather than "permission." Courts have declined to rule on the law's constitutionality each time a related case was brought before them.

Abraham Lincoln's missing bodyguard

The night President Abraham Lincoln was shot, his bodyguard John Frederick Parker was late for his shift—and reportedly left his post to drink at the bar. Infamous assassin John Wilkes Booth entered the booth at Ford's Theater where the president sat while Parker was absent, leading to one of the United States' greatest political tragedies. Read more about the troubled history of Parker here.

The Barbary Wars were an early test of whether a president could wage war without a formal declaration from Congress

Jefferson sent naval forces against North African pirates without a congressional declaration of war, acting under his own authority. Years later, Madison took the opposite approach and formally sought congressional authorization.

In the 1930s, Congress nearly passed a constitutional amendment requiring a national vote before declaring war

The Ludlow Amendment, proposed amid rising isolationism after World War I, would have required a national referendum before Congress could declare war, except in cases of direct attack. It was defeated 209 to 188 in 1938 after Roosevelt lobbied against it.

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.

Congress descended into fistfights, duels, and violence before the Civil War

In the decades before the Civil War, members of the United States Congress carried weapons, assaulted colleagues, and, in one case, a congressman killed another in a duel. The violence was driven largely by sectional conflict over slavery and foreshadowed the nation's descent into war.

See some of the most controversial pardons in presidential history

From Lincoln's selective commutations of Dakota men after an 1862 uprising, to Ford's pardon of Richard Nixon after Watergate, and Bill Clinton's final-day clemency decisions, pardons have long sparked fierce debate over justice, political favoritism, and presidential power.

Abraham Lincoln's election in 1860 triggered a cascade of Southern secessions and the formation of the Confederacy, culminating in the Confederate attack on Fort Sumter in Charleston, South Carolina.

Was the Gettysburg Address written on the back of an envelope?

Abraham Lincoln, the 16th president of the United States, wrote his famed Gettysburg Address on a train car. Actually, he had a version of it ready a few days before. Well, really, he came up with it on the spot. Rumors about the speech's creation abound. This 1909 article walks readers through evidence Lincoln's speech was carefully planned and written in Washington, DC (in pencil).

Listen to a widely lauded historical fiction podcast about the manhunt and power struggle that gripped the US after President Abraham Lincoln's assassination.

Abraham Lincoln had to sneak into Washington, DC, in disguise for his 1861 inauguration after a detective uncovered a plot to assassinate him in Baltimore.

Explore early Thanksgiving documents, from recipes to early proclamations

History buffs will love this trove of original documents related to the Pilgrims and Thanksgiving, including 18th-century recipes, one of Sarah Josepha Hale’s appeals to President Lincoln to establish the national holiday, and a copy of Abraham Lincoln’s original 1863 Thanksgiving Day Proclamation. You can also find illustrations and photos of historical Thanksgiving celebrations over the years.

President Abraham Lincoln was inspired by a novel to create the holiday

A writer and abolitionist from New Hampshire, Sarah Josepha Hale was instrumental in cementing many of the Thanksgiving traditions we celebrate today. Her 1852 novel "Northwood, a Tale of New England," described a feast with a roasted turkey, stuffing, plum pudding, and pumpkin pie. She wrote dozens of editorials and letters to politicians campaigning for the day to become a national holiday. In 1863 she was finally successful in convincing President Lincoln to make it official.

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.

Congress has unsuccessfully voted on war powers resolutions over Trump's military operations in Venezuela and Iran

After Trump ordered unilateral military operations in both Venezuela and Iran without congressional authorization, lawmakers from both parties introduced war powers resolutions to block further action. Each effort failed, with Republican majorities largely supporting the president.

The opposition party to the president first delivered a televised response in 1966

Television networks first granted airtime to the out-of-power party in 1966, with Republicans Everett Dirksen and then-Representative Gerald R. Ford delivering the inaugural response. See a list of each opposition response to the State of the Union since then.