What doctrine stated that the exclusion of slavery in a territory could be determined by voters' refusal to protect slave property?

The Freeport Doctrine, articulated by Stephen A. Douglas during a debate with Abraham Lincoln in 1858, posits that the status of slavery in a territory should be determined by the local settlers themselves. Specifically, Douglas argued that if the residents of a territory did not enact and uphold laws protecting slave property, slavery could effectively be excluded, even if it was not formally prohibited. This doctrine was a significant turn in the debate over slavery, as it emphasized popular sovereignty—the idea that the authority of the government and its laws comes from the consent of the governed—and provided a practical approach to resolving the contentious issue of slavery's expansion into new territories. Douglas's stance highlighted the tensions between different views on slavery and showcased how local decisions could influence national policies, making it a pivotal moment in the lead-up to the Civil War.