1. whose support of slavery led them to disavow their loyalty to the united states?

 Southern states, which seceded from the United States to form the Confederate States of America.

History/context:

The election of 1860 was focused on issues of slavery and states rights.  As reported by the West Virginia Dept. of Arts, Culture, and History, "Abraham Lincoln, the Republican Party's nominee in 1860, was seen as a moderate on slavery, but Southerners feared that his election would lead to its demise, and vowed to leave the Union if he was elected."  

Lincoln was morally opposed to slavery, but he also recognized that slavery was permitted by the existing law of the land, the US Constitution. So Lincoln's initial position on slavery was to stop the spread of it.  

In the South, however, many feared a much more activist agenda from Lincoln and the Republicans.  According to the History Channel, "The election of Abraham Lincoln was labeled an act of war by some Southern politicians, who predicted armies would come to seize slaves and force white women to marry black men."   So as soon as Lincoln was elected, planning for secession began to occur in states across the South.  By February, 1861, seven states had succeeded.  Representatives of those seven states (South Carolina, Mississippi, Florida, Alabama, Georgia,  Louisiana, and Texas) met in Montgomery, Alabama, and formed the Confederate States of America.  Four more states joined the Confederacy later in 1861:  Virginia, Arkansas, North Carolina, and Tennessee.

lincoln declared that slavery should not be allowed to spread into the new states, and of course this angered the south at the time.