This quote from lincoln's speech to congress following the battle of ft. sumter indicates that a primary objective of the union war effort was to

The primary objective of the Union war effort was to PRESERVE THE UNION OF STATES UNDER THE CONTROL OF THE FEDERAL GOVERNMENT. 
One of the principal aim of the Sumter battle is to preserve the existence of the United States as a nation; it is meant to deter other states from breaking away from the Union for any reason.

Bbecause the jim crow laws were made to make voting difficult for african americans