Compromise of 1850 set Texas's boundaries at their present form. U.S. Senator James Pearce of Maryland drafted the final proposal where Texas ceded its claims to land which later became half of present-day New Mexico, a third of Colorado, and small portions of Kansas, Oklahoma, and Wyoming to the federal government, in return for the assumption of $10 million of the old republic's debt. Post-war Texas grew rapidly as migrants poured into the cotton lands of the state. They also brought or purchased enslaved African Americans, whose numbers tripled in the state from 1850 to 1860, from 58,000 to 182,566. Civil War to late 19th century Texas was at war again after the election of 1860. At this time, blacks comprised 30 percent of the state's population, and they were overwhelmingly enslaved. When Abraham Lincoln was elected, South Carolina seceded from the Union. Five other Deep South states quickly followed. A state convention considering secession opened in Austin on January 28, 1861. On February 1, by a vote of 166–8, the convention adopted an Ordinance of Secession from the United States. Texas voters approved this Ordinance on February 23, 1861. Texas joined the newly created Confederate States of America on March 4, 1861, ratifying the permanent C.S. Constitution on March 23. Not all Texans favored secession initially, although many of the same would later support the Southern cause. Texas's most notable Unionist was the state governor, Sam Houston. Not wanting to aggravate the situation, Houston refused two offers from President Lincoln for Union troops to keep him in office. After refusing to swear an oath of allegiance to the Confederacy, Houston was deposed as governor. Around 2,000 Texans served in the Union Army, with a large contingent of recent German immigrants in Texas Hill Country being a Unionist stronghold. While far from the major battlefields of the American Civil War, Texas contributed large numbers of soldiers and equipment to the rest of the Confederacy. Union troops briefly occupied the state's primary port, Galveston. Texas's border with Mexico was known as the "backdoor of the Confederacy" because trade occurred at the border, bypassing the Union blockade. The Confederacy repulsed all Union attempts to shut down this route, but Texas's role as a supply state was marginalized in mid-1863 after the Union capture of the Mississippi River. The final battle of the Civil War was fought at Palmito Ranch, near Brownsville, Texas,