Border Showdown

The Border War (alternatively, Border Showdown) is the name of the rivalry between athletic teams from the University of Kansas and University of Missouri, the Kansas Jayhawks and the Missouri Tigers respectively. Athletic competition between the two schools began in the 1890s when both schools were in the Western Interstate University Football Association. From 1907 to 2012 both schools were in the same athletic conference and competed annually in all sports. Sports Illustrated described the rivalry as the oldest (Division I) rivalry west of the Mississippi River in 2011, but it has been dormant since Missouri departed the Big 12 Conference for the Southeastern Conference on July 1, 2012. Despite overtures from Missouri to continue athletic competition, no further games have been scheduled between the two schools.

The rivalry has historic roots in the often violent relationship between the states of Kansas and Missouri, including guerrilla warfare between the states before and during the American Civil War.

Many believe the rivalry can trace its history to open violence involving anti-slavery and pro-slavery elements that took place in the Kansas Territory and the western frontier towns of Missouri throughout the 1850s. These incidents were attempts by some Missourians (then a slave state) to influence whether Kansas would enter the Union as a free or slave state. The era of political turbulence and violence has been termed Bleeding Kansas. When the Civil War began, the animosity that developed during the Kansas territorial period erupted in particularly vicious fighting. In the opening year of the war, six Missouri towns (the largest being Osceola) and large swaths of western Missouri were plundered and burned by various forces from Kansas generically termed jayhawkers. These attacks led to a retaliatory raid on Lawrence, Kansas two years later (Lawrence Massacre), which led to General Order No. 11 (1863), the forced depopulation of several western Missouri counties. The raid on Lawrence was led by William Quantrill, a Confederate guerrilla born in Ohio who had formed his bushwhacker group at the end of 1861. When the Civil War began, Quantrill was a resident of Lawrence, Kansas teaching school.

...
Wikipedia