This essay discusses British emancipation's influence on antislavery political and constitutional development in the United States during the pivotal decade 1833-1843. The Slavery Abolition Act of 1833 radically revised the Atlantic legal regime embodied in the law of nations. Because the U.S. Constitution had absorbed much of the law of nations, Britain's radical alteration of that regime rippled through the American constitutional system, highlighting dormant tensions in American law and contributing to the rise of diametrically opposed pro- and antislavery constitutional doctrines at the fringes of American politics. In the aftermath of 1833, antislavery forces--and not just radical abolitionists--moved to integrate the United States to Britain's new order while respecting the "peculiar" compromises in the Constitution, reading those provisions narrowly against universal principles. Their labors produced a formidable American strain of the famous freedom principle that would become the backbone of antislavery politics up to and through the Civil War.