Final answer:
The proslavery forces from Missouri that went to Kansas in 1856 through 1858 were known as Border Ruffians. They engaged in voter fraud and illegal vote counting to gain an advantage in the territorial elections.
Step-by-step explanation:
The proslavery forces from Missouri, who went to Kansas in 1856 through 1858, were known as Border Ruffians. They were individuals who crossed the border to vote in Kansas with the intention of influencing the popular-sovereignty rule of the territories. Border Ruffians gained an advantage in the territorial elections through voter fraud and illegal vote counting. They were opposed by the majority of Free Soilers who were against the expansion of slavery into Kansas.