The holiday was declared by Abraham Lincoln as mentioned in 1863, but by 1864 there was much more going on for the holiday. Also the holiday was centered around the war.
In the various pictures in this cartoon there were some of the evil confederates, the peace keepers, the sailors, and thanks to Maryland, for freeing her slaves. (Not that they wanted too!)
Lincoln would die the following April, and the holiday would take on a more thankful, rather than militaristic stance after his administration.