The Kansas-Nebraska Act was supported by and seen as an advantage to

The Kansas-Nebraska Act let settlers in Kansas and Nebraska decide whether to allow slavery through popular sovereignty. Supporters of slavery in the South saw this as an opportunity to expand slavery into new territories. The act also encouraged proslavery border ruffians from Missouri to influence events in Kansas, but the broad group that benefited politically was supporters of slavery in the South.

AI-written and checked against the verified answer.