Very few who read the history of the American Republic can fail to be stirred by the great political debate which accompanied and followed the war with Mexico. The Mexican War was a victorious war, yet it was a war that created great tensions in American politics. Anti-slavery men in the North opposed the war as an expansionist conspiracy on the part of the slaveowners of the South. Henry David Thoreau spent a day in jail for refusing to pay taxes that might support such an unjust enterprise and then wrote Civil Disobedience to explain his philosophy of freedom. James Russell Lowell assailed the territorial gains of the Mexican War in The Biglow Papers with such verses as:
They just want this Californy So's to bring new slave states in To abuse ye, an" to scorn ye An' to plunder ye like sin.
In the Congress, anti-slavery Democrats and Whigs rallied behind a proposal known as the Wilmot Proviso. When President Polk asked for an appropriation of two million dollars for the purchase of territory from Mexico, Representative David Wilmot of Pennsylvania sought to attach to the appropriation bill a proviso to the effect that .neither slavery nor involuntary servitude shall ever exist" in any territories so acquired. David Wilmot became a hero overnight in the North and every northern legislature except one endorsed his Proviso. The Proviso was defeated in the Congress, but it became a burning political issue in the campaigns after 1846. Indeed, in 1848, a third party calling itself the Free Soil Party was formed by a coalition of old abolitionists who had supported the Liberty Party in 1840 and 1844, and "Conscience Whigs" and "Barnburner Democrats" who accepted the free soil principles of the Wilmot Proviso.
At the same time, debates continued to rage in the Congress over the issue posed by the Wilmot Proviso. As these arguments became more heated, sectional positions began to harden, particularly at the extremes. Northern antislavery men took the position that Congress had the moral duty to prohibit slavery in the territories of the United States; freedom was in harmony with our national purposes, slavery was a sectional institution which must be contained in the states where it already existed. Southern fire-eaters countered with the claim that Congress had no power to prohibit slavery in the territories, instead it had a plain constitutional duty to protect slavery in the territories held by the states in common.
The debate became more than an indoor sport in the halls and taverns of Washington during the first year of Zachary Taylor's administration. The gold discoveries in California and the spectacular rush of the "forty-niners" from every part of America to the stream beds on . . .