Why was the Kansas-Nebraska At of 1854 different from the earlier compromises of 1820 and 1850?​

The Kansas-Nebraska Act allowed each territory to decide the issue of slavery on the basis of popular sovereignty. Kansas with slavery would violate the Missouri Compromise, which had kept the Union from falling apart for the last thirty-four years. ... The Missouri Compromise had prevented this from happening since 1820.

disease was the number one killer of native peoples. they had had little exposure to the diseases of europe. this led to some villages being almost completely wiped out and some tribes destroyed.