Some "border Ruffians" invaded the State in order to force the election of a pro-slavery legislature.
A series of violent civil confrontations happened then, between the 1854 to 1861, involving groups that were either pro or against slavery, to decide if Kansas would join the Union as a free State or a Slaver State.
These conflits became known as Bleeding Kansas.
On January 29, 1861, Kansas joined the Union as a free State.