What would be a motivating reason why abolitionists opposes annexation of new western territory during the early 1800s?

Maybe " If  they seize this territory, to what effect of the people we 'fight' for will this go into reason?",then,"They might make it a market, or even a center of slavery! We need to stop this." or at least in the words of a speech.

the correct answer is: the fact that the anti-federalist papers were considered poorly written.

a phrase from a poem by ralph waldo emerson about the battle of lexington and concord. emerson's words read, “here once the embattled farmers stood / and fired the shot heard round the world.”