USA-US cover of civil war stamps

April 12, 1861, Fort Sumter was fired at the South, known as the Battle of Fort Sumter. Later, U.S. President Abraham Lincoln declared war on the South, the Civil War.

First Battle of Manassas (First Battle of Manassas), also known as the Battle of the first Niuben River (First Battle of Bull Run) in July 21, 1861 in Manassas, Virginia, and Niuben Near the river, is the first major battle in the Civil War. 

Many thanks to Candy54449.