Background

In 1839, the term “manifest destiny” was first mentioned in a newspaper article by the journalist John L. O’Sullivan. The term became a widely-held proposition that the settlement of the United States was destined to expand across the North American continent and create a country “from sea to shining sea.” The idea was partly responsible for American expansionism, especially in the two decades between 1840 and 1860.

In 1845, Sullivan published an essay entitled “Annexation” and urged the US to annex the Republic of Texas because “it was our destiny to overspread the continent allotted by Providence for the free development of our yearly multiplying millions.” In 1845, after the annexation of Texas to the Union, Sullivan urged the US government to dispute British claims to the northwest and argued that the US should eventually annex “the whole of Oregon,” meaning the Oregon Territory. He argued that Great Britain would not spread democracy, and therefore, their claim to the Oregon Territory should be challenged. The strategy was that American emigrants would move to the northwest and implement republican democratic values by setting up government, and then seek admission to the Union, just as Texas had done. This would not require the involvement of either the US government or the military. In other words, the settlers would establish American government on the ground before the actual American government got involved.

In the summer of 1845, President James Polk renewed former President Tyler’s proposal to the British to divide the Oregon Territory in half along the 49th parallel, the approximate border between the US and Canada today. When the British refused to accept the offer, American expansionists responded with the slogans “The Whole of Oregon or None!” and “Fifty-Four Forty or Fight!”, referring to the southern border of the territory. In 1846, the British agreed to accept the divide at the 49th parallel, but only after President Polk had threatened to terminate a joint-occupation agreement that had kept the peace for some years.

The lofty ambitions and visions of the expansionist, however, came up against a more fundamental foundational issue of the young republic — slavery. Up to the 1840s, the country had been careful to add as many slave states as free states. Southern senators and representatives jealously protected this balance of slave and free states in Congress. But the expansionism of the Polk Administration and the success of the manifest destiny advocates was upsetting that balance.

When Texas was admitted as a slave state in 1845, it was a triumph for the slave advocates. But the Mexican American War that followed in 1846-48, brought California and the southwest territories into the Union and most of the western territories were choosing to be admitted as free states. In response, representatives from slave states argued that the US should acquire more Mexican territory, hoping that they could create slave states south of Texas. But the American public was unlikely to support another war on Mexico just to gain territory so there would be a balance of slave and free states.

Matters were further aggravated by the growing abolitionist movement and the Wilmot Proviso. It was a piece of legislation introduced in 1847 by Senator David Wilmot of Pennsylvania that confirmed free state status to California and all of the newly acquired territories in the southwest: “Provided, That, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the moneys herein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime, whereof the party shall first be duly convicted.” The Wilmot Proviso created even more disagreements and tensions in Congress.

In 1849, before this proviso could be adopted, President Polk mentioned in his Farewell Address that gold was discovered in California. The news spread fast and thousands of settlers arrived after 1849 by overland journey or by ship around the Cape Horn in California. Most of these new settlers wanted admission as a state and a free state at that. Thus, circumstances on the ground allowed the advocates of manifest destiny to spread the American nation across the continent and the abolitionists to establish the West as a free state zone.

The sources are excerpts from the speeches of prominent expansionists and prominent Congressmen from slave states arguing against expansion.