Peculiar Institution.

The most significant federal slavery cases in the years after 1815 grew out of the deepening problem that some jurisdictions permitted slavery while others did not. Congress had prohibited American participation in the international slave trade as of 1 January 1808. All of the states north of the Mason-Dixon Line had abolished slavery since the Revolution, although the plans of gradual emancipation adopted in New York and New Jersey left some African Americans in bondage. The Northwest Ordinance had excluded slavery from the territories north of the Ohio River (now beginning to enter the Union as states), but the institution had taken root in the Southwest, and a conflict was looming over the status of slavery in the Louisiana Purchase territory. Lord Mansfield's seminal decision in Somerset's Case (1772) provided the basic legal framework for addressing conflicts between jurisdictions that barred slavery and the increasingly...