ON THIS DAY ·
United States declares war on Mexico
Congress declares war on Mexico, two days after President Polk claims Mexico has “shed American blood upon the American soil” in land both countries claimed.
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The moment in context
In the 1840s, Americans traveled west in growing numbers, and expansionists expected the government to secure the lands they entered. They called their cause Manifest Destiny: Providence, or God’s plan, had supposedly assigned the continent to the United States. This promise of national greatness carried a racial assumption that white Americans should rule. President James K. Polk made expansion a policy. Texas, a slaveholding republic since its break from Mexico in 1836, entered the Union in 1845 by a joint resolution of both houses, after the Senate rejected an annexation treaty. Britain and the United States divided Oregon at the 49th parallel, now the Canadian border; its hatching disappears from the map in June 1846.
From Mexican–American War, chapter 1 of The American Civil War, 1840–1877 (JUL 1848).
Teach this in 5 minutes
- Why it happened — Land hunger and an ideology of destiny. The brown arrow follows the Oregon Trail, traveled by thousands in the 1840s. As settlers moved west, they looked to Washington to secure the land…
- The turn — The Wilmot Proviso, 8 August 1846. David Wilmot was a first-term Pennsylvania congressman when, on the night of 8 August 1846, he added a sentence to a bill granting Polk $2 million…
- What it changed — Free soil becomes a party. Opposition to slavery’s expansion could unite Northerners who were not prepared to challenge slavery where it already existed. Their cause was free…
Then ask the room: Was the Mexican War a war for slavery? The argued answer is on the chapter page →
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