Aces and Eights takes modern ideas, groups or characters and places them in the American Old West, but specifically omitting the existence of the SCP Foundation as an organization only. The introduction to the canon showcases a article regarding the in-universe American Civil War.
It shows the historical surrender of General Lee (General of the Confederate Army) to General Sherman (General of the Union Army), ending the civil war with a Union victory. It also reveals the ahistorical nature of the Battle of Gettysburg where the Confederate Army (with some alleged help from anomalous sources) destroyed the Union Army. The terms of the surrender are also more favorable to the Confederacy, and President Abraham Lincoln also resigns. An event titled the "Razing of Baltimore" is also referenced.
The rest of the universe is built within the tales.