Demigod Civil War

The Demigod Civil War was a battle between Roman and Greek demigods in 1864, involving a battle in the woods of Camp Half-Blood.

History
The battle was three days long. It was fought with terrible losses on both sides. Horrified by the bloodshed, the gods forced the Roman and Greek demigods to opposite sides of the country and manipulated the Mist to be strong between the two camps so that the two groups would never meet and the incident could never repeat. The war mirrored the American Civil War. It is unknown who won the war, if there was a winner at all.

The Lost Hero
Leo finds Bunker 9 which was used during the war as a base by the Hephaestus or Vulcan demigods, depending on which group used the bunker. It was hidden and forgotten until he found it and revealed it to the rest of Hephaestus' Cabin, along with Jason, Piper, and Chiron. Chiron is revealed to have known about the cabin and tells the demigods a small amount of information about the war and how conflicts in the Mortal world can carry over to the world of the gods and demigods. Inside there are hundreds if not thousands of schematics, project, and blue prints (one was a blue print of the Argo II) created and was used as a base of operations during the last demigod war in 1864.

The Son of Neptune
Reyna mentions that the Greeks and Romans have fought each other in recent times to Percy, the last being the American Civil War.