Southerners saw Texas as prime land for the expansion of the plantation system and slavery, even when Texas was still part of Mexico. American settlers arrived in droves, so many that they quickly outnumbered Mexican settlers. Fearing that Mexico would free their slaves, Texans proclaimed their independence on March 2, 1836.

When the resulting fight with Mexico was over, Texans wrote a constitution for their Republic of Texas that made their pro-slavery stance perfectly clear. The Texas constitution declared slavery legal in no uncertain terms and at the same time banned free African-Americans from settling in Texas. Along with formalizing their pro-slavery views, Texans were also looking ahead to eventually joining the United States, and they wanted to be very clear which side of the divide they were on.

That divide, of course, was between the North and the South. Tensions were already escalating in the 1830s and 1840s, and government leaders were trying to be especially careful to preserve a balance of power between the two regions. They were, therefore, hesitant to annex the clearly pro-slavery Texas, a move which would please the South but aggravate the North. President Andrew Jackson didn't even recognize the Republic of Texas until he was ready to leave office, and his successor, Martin Van Buren, did his best to ignore the annexation issue. In fact, Texas did not enter the Union until December 29, 1845. Its constitution was clear about Texans' priorities, but it also delayed Texas becoming a state.