This article is from the U.S. Civil War FAQ, by Justin M. Sanders firstname.lastname@example.org with numerous contributions by others.
1. The United States never declared war. This was in keeping with its
position that the rebel states did not form a new nation, rather they were
states in which a rebellion was taking place. Abraham Lincoln issued a
Proclamation that an insurrection existed in the states of SC, GA, FL, AL,
MS, LA, and TX on 15 Apr 1861 (Messages & Papers of the Presidents, vol. V,
p3214). He also proclaimed a blockade of Southern harbors on 19 Apr
1861, and the date of this proclamation was taken by the Supreme Court in
several cases to be the official beginning of the insurrection.
2. The Confederate States passed "An Act recognizing the existence of
war between the United States and the Confederate States" on 6 May 1861.
This act exempted MD, NC, TN, KY, AR, MO, DE, and the territories of AZ
and NM, and the Indian Territory south of KS.
Sources: McPherson, Battle Cry of Freedom; Official Records, Ser. IV,