Manifest destiny fueled US aggression against 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.

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.

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.

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.

The Monroe Doctrine helped lead to the American occupation of territory abroad

This podcast explores how the policy motivated a century of US military intervention throughout Latin America, the Caribbean, and the Pacific—covering the annexation of Hawaii, the Spanish-American War, and occupations of Cuba, Haiti, and Panama.

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.

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

As a freshman congressman, Abraham Lincoln introduced the “Spot Resolutions,” demanding President Polk prove that Mexico had attacked on US soil. This constituted Lincoln’s first major political stand and highlighted growing dissent over the war.

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.

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.

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 US won every major battle of the Mexican-American War

Despite being outnumbered in key engagements, US forces defeated Mexican armies across every major front. Superior training, leadership, and logistics allowed the US to win decisively—capturing Mexico City without losing a single major battle.

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.

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 Roosevelt Corollary transformed the Monroe Doctrine from a defensive warning into a rationale for US military intervention

In 1904, President Theodore Roosevelt declared that the US had the right to exercise international police power in Latin America. Over the following two decades, the US intervened militarily in the region about a dozen times—often enough that Marines became known locally as "State Department troops."

France invaded Mexico to install a puppet monarchy and recover debt

Napoleon III used Mexico's default on foreign loans as cover for a larger imperial ambition: overthrowing President Benito Juárez's government and installing a French-backed monarchy. The Mexican army's surprise victory at Puebla helped delay those plans by nearly a year.

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.

The US Army inherited the Apache Wars after the Mexican-American War

The resolution of the Mexican-American War inserted the US Army into an ongoing conflict between Apache groups and outside powers—transforming local resistance into a decades-long struggle against American expansion known as the Apache Wars.

A wave of Latin American independence movements most likely prompted the Monroe Doctrine

Between 1810 and 1822, many Latin American colonies separated from Spanish rule, 10 in the last two years. Concerns that Spain and its European allies might try to regain these republics were a main reason behind Monroe's declaration.

Irish immigrants deserted the US Army to fight for Mexico

During the Mexican-American War, hundreds of Irish Catholic immigrants—facing discrimination in the US Army—defected to Mexico and formed the Saint Patrick’s Battalion. Though many were captured and executed, they remain honored as heroes in Mexico.

See the path Spanish conquistadors took to conquer the Aztecs

Spanish expeditions reached central Mexico as the Aztec Empire was expanding its influence. After securing bases in the Caribbean, they advanced west into Aztec territory, triggering a cascading conflict depicted in this interactive map and timeline.

Explore the social and cultural history of the Mexican-American War

Historian Peter Guardino joins host Don Wildman to explore how the war shaped ordinary lives on both sides of the border. Drawing from The Dead March, the episode reveals how culture, class, and ideology shaped the conflict and its consequences.

President Trump invoked the Monroe Doctrine in 2025, announcing a new 'Trump Corollary'

On Dec. 2, 2025, the 202nd anniversary of the doctrine, President Donald Trump issued a proclamation reaffirming US "dominance" in the Western Hemisphere. His administration's national security strategy officially codified the "Trump Corollary," stating that the US would prevent non-hemispheric powers from gaining strategic influence in the Americas.

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.

Hear the reasoning behind Trump's resurrection of the Monroe Doctrine in 2025.

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.

US military professionalism gave America a decisive edge in the war

The professionalism and engineering expertise of West Point–trained officers—like Grant, Lee, and Meade—gave the US a major advantage in the Mexican-American War, helping them win every major battle.

The Monroe Doctrine was designed to keep Europe out of the Americas

First articulated in 1823 by President James Monroe, the doctrine declared the Western Hemisphere off limits to European colonization. It has since been invoked to justify US military interventions in Latin America, from Teddy Roosevelt's takeover of Venezuela to George H.W. Bush's arrest of Panama's leader Manuel Noriega.

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.

Jefferson feared European control in the West of North America

Jefferson pushed for the Louisiana Purchase to prevent France or Spain from dominating the western frontier, securing control of the Mississippi River and vast lands that he felt were essential to America’s strategic and economic future.

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.

How the US entered WWI in 1917

Originally taking a position of neutrality during the course of World War I, the United States of America eventually relented. Entering the war in 1917, support for the British and French had risen and Americans were incensed by Germany's overtures to Mexico and U-boat attacks that sank ships and ended American lives. See how and why the US entered WWI in this article.

The British Royal Navy—not the US military—enforced the Monroe Doctrine for most of the 19th century

In the early to mid-1800s, the US lacked the ships and military power to prevent European nations from colonizing the Americas. Britain enforced this to protect its commercial interests by keeping rival European powers out of Latin America.

As president, Thomas Jefferson expanded federal power despite opposing centralized authority

Although Jefferson argued for limited national power, his presidency expanded federal authority through actions such as the Louisiana Purchase, territorial governance, and federal enforcement—reflecting a pragmatic departure from his earlier strict interpretation of the Constitution.

Some historians claim that Mexico's victory at Puebla may have prevented France from arming the Confederacy

According to some experts, Napoleon III planned to ship weapons from Mexico to Confederate forces to break the Union naval blockade. The delay caused by the Battle of Puebla meant French resources didn't reach the Texas border until after the Union Army's decisive victory at Vicksburg.

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.

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.

Before World War II, the US was a Pacific power

Decades before Pearl Harbor, the US held major Pacific territories—Hawaii, the Philippines, Guam, American Samoa, and numerous island bases—giving it strategic reach across the western Pacific. This presence increasingly overlapped with Japan’s imperial ambitions in the region, contributing to rising tensions.

Learn about the history of the Monroe Doctrine

CBS Sunday Morning explores the origins of the Monroe Doctrine, tracing how a 19th-century warning against European intervention shaped US foreign policy and influenced America’s role in the Western Hemisphere for generations.

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.

Hear about why Europe obeyed the Monroe Doctrine, despite American military weakness

This podcast explores the European background of the Monroe Doctrine, highlighting France's efforts to install aristocratic Bourbon monarchs in the newly independent Latin American republics—and how US opposition, British threats, and Spanish resistance ultimately disrupted those plans.

Japan's imperial expansion in Asia in the 1930s set the stage for war with the US.

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The Mexican-American War led to the birth of the Associated Press

To cover the distant war efficiently, rival New York newspapers pooled resources to share reports from the front—forming what became the Associated Press. The war marked a turning point in how Americans received real-time news about foreign conflicts.

The power and influence of the American presidency have expanded significantly over time—far beyond what the founders envisioned.

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.

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.

Presidents have often used military force without formal declarations of war

Although the Constitution grants Congress the power to declare war, American presidents have repeatedly ordered military action without formal declarations. These precedents have expanded executive authority in national security beyond what the framers likely envisioned.

A formal declaration of war automatically triggers hundreds of statutes granting the president sweeping domestic authority

Beyond authorizing military force abroad, a formal declaration activates a wide range of domestic powers, including authority over enemy property, trade restrictions, and emergency economic authority. It also waives the 60-day time limits under the War Powers Resolution.

One Native leader tried to save his people's land by building a nation

As the US pushed westward in the 19th century, one leader of the Ojibwe people fought back not with arms but with politics, seeking to preserve his people's territory and way of life by building a formal Native nation capable of negotiating on equal footing with the US government.

The intellectual architect of the Monroe Doctrine was Secretary of State John Quincy Adams, not Monroe

Adams, the main foreign relations authority in the Cabinet, shaped the key parts of the Monroe Doctrine speech. He advocated for a unilateral American declaration to warn European powers, rejecting a potential joint statement with Britain favored by some Cabinet members.

The diplomat who implemented Monroe's policy introduced the poinsettia to the United States

Joel Roberts Poinsett, appointed as the first US minister to Mexico in 1825 following the doctrine's announcement, took cuttings of a vibrant Mexican plant called the cuetlaxochitl during his time there. Americans loved the foliage and named it after him.