American Civil War

The American Civil War (1861—1865), also known as the War Between the States and several other names, was a civil war in the United States of America fought for the freedom of slaves.

Description
Eleven Southern slave states declared their secession from the U.S. (the Union) and formed the Confederate States of America (the Confederacy). Led by Jefferson Davis, they fought against the the northern states federal government (the Union), which was supported by all the free states and the five border slave states in the north. The U.S. federal government was led by the 16th President of the United States of America, Abraham Lincoln together with Chiron; Camp Half-Blood activities director.

There is only one known demigod involved in this war, although numerous children of Athena, and Ares probably fought. Harriet Tubman was a child of Hermes.

The Sea of Monsters
Clarisse helps Percy, Tyson, and Annabeth defeat the Hydra with a Confederate Ironclad warship. The book mentions that in every war, the losing side has to give Ares a small fraction of their dead soldiers, giving Ares control over them.

The Lost Hero
The Roman and Greek demigods had a giant battle that lasted three days in Camp Half-Blood's woods around the time of the American Civil War. The loss of life was so great, the gods were forced to separate them and bind the Mist as tightly as possible so the two sides would forget each other. Chiron told the other campers about Bunker 9, a secret war base used when the Roman and Greek Demigods were fighting each other around the time of the American Civil War when he and the other campers (Hephaestus, Athena, Hypnos, etc) were shown to the bunker by Leo Valdez who opened it after the Quest to save Hera with Jason Grace and Piper McLean.