Manifest Destiny and the Road to War

The phrase 'Manifest Destiny' entered the American vocabulary in 1845, coined by journalist John O'Sullivan to describe what he called the nation's God-given right to expand across the North American continent.

But the ideology was older than the words — woven into American political culture since the Revolution, embedded in the assumption that a republican nation of free farmers would inevitably spread westward until it reached the Pacific.

By the 1840s, thousands of American settlers were already streaming into Oregon Territory and Mexican-controlled California, and the vast province of Texas — which had fought its own revolution against Mexico in 1836 — was agitating for annexation to the United States.

Mexico had never recognized Texan independence and considered annexation an act of war.

The annexation crisis had simmered for nearly a decade. The Republic of Texas applied for U.S. statehood almost immediately after winning independence at San Jacinto in 1836, but the question of admitting a large new slave state kept Congress paralyzed.

The balance of power between slave and free states was the central fault line of American politics, and abolitionists charged that the Texas independence movement itself had been engineered by Southern slaveholders seeking new land for cotton cultivation. Not until 1845, when James K.

Polk won the presidency on an explicitly expansionist platform, did Congress agree to annex Texas — admitting it as the twenty-eighth state in December 1845. Mexico immediately severed diplomatic relations.

The border question transformed a diplomatic crisis into an armed confrontation. Texas claimed its southern and western border ran along the Rio Grande; Mexico insisted the Nueces River, 150 miles to the north and east, was the actual boundary — as it had been under Spanish colonial administration.

President Polk, determined to press the American claim and simultaneously acquire California, ordered General Zachary Taylor to march his 'Army of Occupation' from Corpus Christi to the banks of the Rio Grande in March 1846. To Mexico, this was an invasion.

Taylor's army began constructing Fort Texas directly across from the Mexican city of Matamoros, with artillery trained on the town. The Mexican commander demanded Taylor withdraw. Taylor refused.

On April 25, 1846, a Mexican cavalry force crossed the Rio Grande and ambushed a sixty-three-man American patrol under Captain Seth Thornton, killing eleven and capturing the rest.

When word reached Polk, he had already drafted a war message citing Mexican refusal to pay American financial claims; he now added the Thornton skirmish and sent Congress the famous declaration that 'Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil.

' Congress voted overwhelmingly for war on May 13, 1846 — though skeptics like young Congressman Abraham Lincoln would later demand to know exactly which spot of 'American soil' had been stained with blood, and whether that spot had truly ever been American at all.