Final answer:
Virginia, Arkansas, Tennessee, and North Carolina seceded from the Union in response to Abraham Lincoln's call for 75,000 volunteers following the Battle of Fort Sumter, thus joining the Confederacy.
Step-by-step explanation:
In response to Abraham Lincoln's call for 75,000 volunteers after the Battle of Fort Sumter, several states dissolved their ties with the United States and joined the Confederacy. Virginia voted to secede on April 17, 1861, just two days after the call for volunteers. Arkansas seceded from the Union on May 6, and Tennessee followed on May 7. Finally, North Carolina declared its secession on May 20.
This all occurred during a tumultuous period for the Upper South states, where loyalties were tested following the onset of the American Civil War. Though some states like Delaware, Maryland, Missouri, and Kentucky remained with the Union, the aforementioned states decided to join the Confederacy partially due to Lincoln's call for troops and the increasing tensions surrounding the issues of states' rights and slavery.