Congressman Abraham Lincoln of the House Committee on the Post Office and Post Roads had a seemingly innocuous task: amend a post roads bill by adding routes in rural Georgia and South Carolina. Little did Lincoln know that this bill would spark fierce debate and conflict in the U.S. House of Representatives. The bone of contention? Territorial expansion and the extension of slavery in the aftermath of the Mexican War.
Lincoln and his fellow members of the committee had a clear-cut assignment on the face of it: draft legislation establishing new postal routes for the growing republic. Committee chairman William L. Goggin introduced H.R. 260 on February 29, 1848. The committee then folded Lincoln’s amendments into the bill and reported it back as amended on May 16.
Lincoln, around 1848 (ALPLM)
While Lincoln and the committee members were deliberating, the U.S. Senate was debating the Treaty of Guadalupe-Hidalgo. Signed on February 2 and ratified by the Senate on March 10, this treaty officially ended the war with Mexico. Under its terms, Mexico acknowledged the Rio Grande River as the southern boundary of Texas and ceded 525,000 squares miles of its territory, including parts of present-day Arizona, California, New Mexico, Texas, Colorado, Nevada, and Utah, to the United States.
Acquisition of territory from Mexico raised concerns about the extension of slavery, reigniting sectional animosities and exacerbating lines of fission in the Democratic and Whig parties. Anti-slavery Democrats and Whigs were willing to accept territorial expansion if they also got approval of the Wilmot Proviso, which barred slavery from all territory acquired from Mexico. Conservative and moderate Whigs from the North and South, looking for a way to differentiate themselves from the pro-expansion Democrats, originally opposed taking Mexico’s territory, with or without the proviso. After the war, they reluctantly accepted expansion rather than vote against the treaty ending the war.
Adding fuel to the fire was the unresolved question of the western border of Texas. Texans claimed the Upper Rio Grande as the boundary, including Santa Fe and territory also claimed by New Mexico. Acquiescence of this border would have allowed Texans to take slaves further west into the Mexican cession, pleasing pro-slavery Southern extremists but upsetting devotees of the Wilmot Proviso.
Texas-Mexico border, 1847 (Library of Congress)
It was against this backdrop that the Committee on the Post Office and Post Roads reported back H.R. 260 with amendments. Included was a supplemental postal bill adding routes in Texas to the Rio Grande. This amendment sparked furious disagreement that threatened to scuttle the entire legislation. After additional amendments, the House voted to finalize the bill’s language, but several Whig representatives moved to re-consider this vote, arguing in part that the bill effectively extended the boundary of Texas to Santa Fe and the Upper Rio Grande, opening these acquisitions to slavery and blunting the Wilmot Proviso. Goggin proposed a proviso disavowing any opinion on the boundary issue as a means to save H.R. 260, but the House refused to take further action.
Mexico and the United States, meanwhile, had exchanged ratifications, and the Polk administration proclaimed the treaty on July 4. With the southern boundary decided, Lincoln and his fellow committee members moved to save the postal route legislation. On July 19, Lincoln introduced H.R. 599, which was the same bill as H.R. 260, with the exception of a proviso added at the end as follows: “Provided, That nothing in this act contained, shall be so construed as to express any opinion as to the true boundary of any State or Territory therein named.” This broke the deadlock. The House immediately passed the bill, and the Senate followed suit on August 11. President Polk signed the act into law three days later.
Detail from "A Bill to Establish Certain Post Routes" (Papers of Abraham Lincoln)
The postal routes controversy plunged Lincoln into the deep end of sectional controversy over the expansion of slavery. His introduction of H.R. 599 allowed the Post Office Department to establish postal routes in territory acquired from Mexico without furthering agitation over the western boundary of Texas. (Texas later gave up its claim to territory to the Upper Rio Grande in exchange for $10 million.) The conflict over postal routes, however, was a prelude to further sectional conflict over slavery in the new territory. The divisions threatened to explode into war but the threat was defused – for a few years, anyway – by the Compromise of 1850.
Director, Papers of Abraham Lincoln