OpenStax
Open Stax: The Filibuster and the Quest for New Slave States
This section of a chapter on "The Antebellum South" explains the expansionist goals of advocates of slavery and describes the filibuster expeditions undertaken during the antebellum era.
Other
Course Notes: Us History: 1840 1877: Expansion and Slavery
A list with short descriptions of the issues and events that impacted the expansion of the frontier, with slavery being the most significant issue.