With the republic largely populated by American emigres, those on both sides of the Sabine River border between the U.S. and Texas deemed it inevitable that Texas would join the United States, but this would anger Mexico, which considered Texas a breakaway province, and threatened war if the United States annexed it. Jackson, as president, had recognized Texas independence, but the initial momentum toward annexation had stalled.[73] Britain was seeking to expand her influence in Texas: Britain had abolished slavery, and if Texas did the same, it would provide a western haven for runaways to match one in the North.[74] A Texas not in the United States would also stand in the way of what was deemed America's Manifest Destiny to overspread the continent.[75]
Clay was nominated for president by acclamation at the April 1844 Whig National Convention, with New Jersey's Theodore Frelinghuysen his running mate.[76] A Kentucky slaveholder at a time when opponents of Texas annexation argued that it would give slavery more room to spread, Clay sought a nuanced position on the issue. 