Here, I will show many envelopes as I find time. Although they are much more rare, I will also try to include a few confederate envelopes.
Many Civil War Covers, have very beautiful images. Many times, they were printed in multiple colors, and feature patriotic scenes, with the American Flag, Soldiers (including famous leaders of the time), Sailors, Eagles, and other patriotic images.
Some promoted the cause of the Union, and others the cause of the rebellion.
(Just click on the image to see a full size version, and for more details)