Why did the kansas nebraska act upset people?

The Kansas Nebraska Act was adopted in 1854, under President Franklin Pierce's administration. The law opposed the earlier Compromise of 1850 by arguing that the new territories of Kansas and Nebraska (both significantly larger than the present states of Kansas and Nebraska) would be allowed to refer to slavery in spite of the fact that they were north of the latitude set out in the Missouri Compromise. The law annoyed slave opponents at both the Democrats and, above all, at the Whig Party, which in the same year formed the Republican Party on a completely slave-friendly basis.

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