When an anti-slavery speaker came to Lowell in 1834, he drew an angry stone-throwing mob. Mill owners and workers depended on Southern cotton, and anyone who threatened the system was unwelcome. Ever since Slater's cotton mill was established in 1790 and the cotton gin invented three years later, Southern cotton and Northern textiles had had a reciprocal relationship. The North's appetite for raw cotton spurred increased cotton production and the expansion of slavery. Lowell not only bought Southern cotton, but it made"negro cloth" that was sold to plantations. For a few years, the machine shop produced cotton gins sold in the South. Senator Charles Sumner called it an " unholy union ... between the cotton planters and fleshmongers of Louisiana and Mississippi and the cotton spinners and traffickers of New England - between the lords of the lash and the lords of the loom."

Dependence on slave grown cotton and moral indignation over slavery coexisted uneasily in Lowell in the years before the Civil War. Many Lowell residents were uncomfortable enough about slavery that they opposed its extension into western territories. Most, however, fearing the mounting sectional conflict, probably would have supported a compromise that accepted slavery where it already existed. But when war broke out, the Union cause and the abolitionists’ cause merged. Its "Southern connection" broken, the city lined up behind Lincoln's Emancipation Proclamation and the Union war effort.