James L. Roark, et al., eds., The American Promise: A History of the United States, 2nd ed., vol. 1 (Boston: Bedford/St. Martin’s, 2002), 457.
In 1793, a federal law gave muscle to the provision by authorizing slave owners to enter other states to recapture their slave property. Proclaiming the 173 law a license to kidnap free blacks, northern states in the 1830s began passing "personal liberty laws" that provided fugitives with some protection.