Based on the text and the context of John Brown's actions during the Bleeding Kansas period, the most likely answer is:
B) the Free-Staters because they were abolitionists committed to ending slavery.
John Brown was a vehement abolitionist who supported efforts to oppose the expansion of slavery into new territories, and he actively engaged in violent actions against pro-slavery forces to promote the cause of abolition. The Free-Staters were those who fought against the spread of slavery into Kansas, aligning with Brown's goals.