Many people disapproved of the Kansas-Nebraska Act because it repealed the Topeka Constitution.
O the Lecompton Constitution.
the Missouri Compromise.
O the Mexican Cession.

The Missouri Compromise.

Explanation:

The Kansas-Nebraska act repealed the Missouri Compromise and created two new territories where people would vote on whether or not they would be slave or free states. This caused many people to rush into the territories to tip the scales, and that caused the "Bleeding Kansas" incident.

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.