In his 1845 essay called "Annexation", written in support of annexing Texas from Mexico, O'Sullivan argues that the measure should not be understood as an attempt to acquire more slave states for the South. This view was common among Northern Whigs, and was a key reason for the sectional divide over annexation and the Mexican War. Rather, O'Sullivan argued that acquiring Texas would actually result in a decline in slavery throughout the Upper South because the Texas climate, he assured his readers, was far more beneficial to cotton agriculture than anywhere else. He said Texas would serve as a "drain" through which slaves would flow out of the south by creating demand for their labor. Eventually, he said, slaves would be sold into Latin America, which he thought was "the only receptacle capable of absorbing that race whenever we shall be prepared to slough it off." Like many Democrats of his day, O'Sullivan thought the size of enslaved African-American populations stood in the way of emancipation, since he believed that white people could never live in the midst of large masses of freedmen. So rather than an attempt to build up the slave power, O'Sullivan argued that the annexation of Texas in particular, and westward expansion in general, offered a way to rid the nation of slavery. O'Sullivan thought slavery wrong, but did not sympathize with African-Americans themselves. As his language in this essay reveals, his vision was one of a white America, and annexation would make it whiter.