Through the night, day, mud, and dirt, the horses of the Civil war were pushed beyond their breaking point. They carried men from both sides into battle, and just like the soldiers they carried, they never knew what they were about to get into.
It seems to be that the horses who carried soldiers into battle are often overlooked or unmentioned unless of course they were a general's horse such as Gen. Robert E. Lee's Traveller or perhaps Gen. Ulysses Grant's Cincinnati.
It may be that perhaps there are just too many to mention. But that does not mean they should be forgotten. There were well over a million horses used on the Union side alone. In the early stages of the war, more horses than men were killed. In the Battle of Gettysburg alone, there were over 1500 horses and mules killed. The horses were able to withstand shots of small firearms but not of larger guns. That was just over the course of three days and one battle.
These horses were trained to carry a soldier to formation on a battlefield, carry messages, haul artillery and cargo, as well as carry the dead off the field. One might be able to say that if not for the horse, there may not have been a war. The men depended so much on horses that in the Treaty of Appomattox in 1865 at the end of the war, Lee insisted that each Confederate cavalryman be given his horse to take home that they would be able to plant corn in the spring. Without horses, they would have nothing to pull their plows or till their land. This shows the importance of the horse at this time.
At the end of the war, it is estimated that well between 1,000,000 and 3,000,000 horses and mules were killed.