Free-Stater was the name given those settlers in Kansas Territory during the Bleeding Kansas era in the 1850s who opposed the extension of slavery to Kansas.
Many Free-Staters were abolitionists from New England, in part because there was an organized emigration of settlers to Kansas Territory arranged by the New England Emigrant Aid Company beginning in 1854. Other Free-Staters were abolitionists who came to Kansas Territory from Ohio, Iowa, and other midwestern states.
However, the majority of Free-Staters, regardless of where they were from, did not claim to be abolitionists at the outset. Instead, the official Free-State line supported the idea of excluding all African-Americans from the future state of Kansas and did not advocate the abolition of slavery nationwide. What united the Free-Staters was a desire to defeat the proslavery Southern settlers in Kansas Territory on the question of whether Kansas would be admitted to the Union as a slave state. (The Kansas-Nebraska Act of 1854 had left the question open to the settlers in the territory.)
Pro-slavery Southerners in Kansas Territory painted all Free-Staters as abolitionists in order to motivate the South's opposition. However, Eli Thayer and other New England Company leaders denied that they were seeking to abolish slavery, and the failed Topeka Constitution drafted by the Free-Staters in 1855 would have excluded any African-American – slave or free – from settling in Kansas.
As time passed and the violence in Bleeding Kansas escalated, abolitionists became ascendent in the Free-State movement. In 1858, the Free-Staters proposed a second constitution, the Leavenworth Constitution, which banned slavery. (This constitution also failed.)