The First Sack of Lawrence occurred on May 21, 1856, when proslavery men attacked and looted the antislavery town of Lawrence, Kansas. The assault escalated the violence over slavery in Kansas Territory during a period that became known as “Bleeding Kansas.” The sacking coincided with South Carolina congressman Preston Brooks’s scandalous caning of abolitionist Republican senator Charles Sumner, which had occurred on May 20. The two events were paired and dramatized by the national media, constituting turning point in the lead up to the Civil War.

Wilson Shannon was an attorney, the 14th and 16th governor of Ohio, United States minister to Mexico, U.S. congressman, and the second territorial governor of Kansas. He was a leading proslavery figure in early Kansas politics and, despite a short 9.5-month tenure, its longest continuously-serving territorial governor. Despite these successes, the disastrous violence of "Bleeding Kansas" began during his term as territorial governor.

The New England Emigrant Aid Company (NEEAC) formed in response to the Kansas-Nebraska Act of 1854. That bill declared that eligible voting residents in Kansas Territory would determine whether the future state would allow or prohibit slavery as a requisite for admission to the Union, creating what became known as popular sovereignty. Antislavery Northerners denounced the act because it essentially repealed the Compromise of 1820, which barred slavery in the lands attained from the Louisiana Purchase above the 36°30’ parallel, including the area that would become Kansas.