In Kansas, Border Ruffians was the name applied to pro-slavery activists from the slave state of Missouri, who in 1854 to 1860 crossed the state border into Kansas Territory to force the acceptance of slavery there.
Armed Ruffians interfered in territorial elections, and attacked Free-State settlements. This violence was the origin of the phrase "Bleeding Kansas". The Ruffians contributed to the growing sectional tensions, and helped bring on the American Civil War. The Ruffians were driven by the rhetoric of leaders such as U.S. Senator David Rice Atchison (D-Missouri) who called Northerners "negro thieves" and "abolitionist tyrants". He encouraged Missourians to defend their institution "with the bayonet and with blood" and, if necessary, "to kill every God-damned abolitionist in the district." Notably, only a few of the Border Ruffians actually owned slaves; most were too poor. What motivated them was hatred of Yankees and abolitionists, and fear of free blacks living nearby.
The presence of bands of both Kansan and Missourian combatants in the area made it difficult for families on the border to remain neutral.
Kansas Territory was created by the Kansas–Nebraska Act of 1854. The Act repealed the previous Federal prohibition on slavery in that area. Instead, the locally elected territorial legislature would decide.
At this time, many (probably most) of the settlers in Kansas opposed slavery. However, slavery advocates were determined to have their way regardless. When elections were held in Kansas Territory, bands of armed Ruffians seized polling places, prevented Free-State men from voting, and cast votes themselves (illegally, since they were Missourians).
On November 29, 1854, Border Ruffians elected a pro-slavery territorial representative to Congress. On March 30,1855, the Ruffians elected a pro-slavery legislature.
Despite these measures, far more Free-State settlers moved to Kansas than pro-slavery settlers. In 1857, pro-slavery settlers in Kansas proposed the Lecompton Constitution for the future state of Kansas. The Ruffians tried to get the Lecompton Constitution adopted with additional fraud and violence, but by then there were too many Free-Staters there.
The Border Ruffians also engaged in general violence against Free-State settlements. They burned farms and sometimes murdered Free-State men.
Most notoriously, the Ruffians twice attacked Lawrence, Kansas, the Free-State capital. On December 1, 1855, a small army of mainly Border Ruffians laid siege to Lawrence, but were driven off. (This was the nearly bloodless climax to the "Wakarusa War".)
Free-State settlers sometimes struck back. Free-State irregulars (known as Jayhawkers, Redlegs, or Redleggers) attacked pro-slavery settlers and suspected Ruffian sympathizers. Most notoriously, abolitionist John Brown killed five pro-slavery men at Pottawatomie.
Thomas Wentworth Higginson became a founding member of the Kansas Aid Committee in the summer of 1856. During the guerrilla war in the Kansas Territory between proslavery and antislavery settlers, the committee worked to recruit abolitionist settlers, raised funds for them to migrate to Kansas, and equipped them with rifles to use against the “Border Ruffians.” 
During the Civil War
During the Civil War, the violence in this area not only continued, but escalated tremendously. Many of the former Ruffians became pro-Confederate guerrillas. They operated in western Missouri, sometimes raiding into Kansas, and Union forces campaigned to suppress them. Farms were burned and looted. Suspected guerrillas were killed; guerrillas killed Union sympathizers and suspected informers. (See Bushwhacker.)
Many of the Union troops involved were Kansas Jayhawkers, and had deep grudges against Missourians. Jayhawkers destroyed several towns in Missouri, such as Osceola. The destruction of Osceola is depicted in the movie The Outlaw Josey Wales.
- Tom Ward; Carolyn Ward (2002). "Border Ruffians - KS-Cyclopedia - 1912". Archived from the original on 2007-12-06. Retrieved 2007-11-19.
- "Bleeding Kansas: Mid 1850s - Precursor to the Civil War". www.u-s-history.com. 2002–2005. Retrieved 2007-11-19.
- "Bleeding Kansas". Fort Scott National Historic Site. paragraph 1. Archived from the original on 2008-06-21. Retrieved 2007-11-19.
- Poole, W. Scott (2005). "Higginson, Thomas Wentworth". In Finkleman, Paul. Encyclopedia of African American History, 1619–1895: From the Colonial Period to the Age of Frederick Douglass. Oxford. ISBN 9780195167771.
- Bad Blood, the Border War that Triggered the Civil War DVD documentary. Kansas City MO: Kansas City Public Television (KCPT) and Wide Awake Films. 2007. ISBN 0-9777261-4-2