Final answer:
Proslavery forces, including border ruffians, engaged in voter fraud to win territorial elections in Kansas, while antislavery advocates moved in large numbers and received support from northern organizations to counteract and establish an antislavery government.
Step-by-step explanation:
Proslavery and antislavery forces took several actions to sway Kansas to their respective sides. Proslavery advocates from Missouri, labeled as border ruffians, infiltrated Kansas to vote in the territorial elections illegitimately, often by resorting to voter fraud. Winning the elections enabled them to form a proslavery legislature and draft the Lecompton Constitution. Conversely, antislavery forces, supported by northern organizations like the New England Emigrant Aid Society, moved into Kansas to outnumber slaveholders and establish a government in Topeka with intentions to select a new legislature that barred slavery. Tensions between proslavery and antislavery supporters escalated into violence, epitomized by the sacking of Lawrence by proslavery forces and the radical response by antislavery advocates led by figures such as John Brown.