[Galacta7]

This would assume that there is consensus on what the "United States" is. If a significant portion of the US Military feels differently, then a civil war is inevitable. This is what basically happened in the actual American Civil War, as a number of U.S. officers and soldiers formed their own forces (under their new Confederate government) to fight against the United States.

[eric-hu]

My civil war knowledge is limited. Are you aware of what happened to larger assets like cannons and warships?

I imagine today these would be far more of a deciding power than troops.

[Galacta7]

My understanding is that the Confederacy did seize federal armories, navy yards and other military depots located in the South, which would have supplied a non-insignificant amount of small arms and canons. But most of the antebellum industrial capacity for manufacturing more was in the North, so the Union always had a strategic advantage there.

In terms of warships, the CSA did capture and convert existing Union ships in Norfolk, Virginia (despite the Union's efforts to scuttle them as they withdrew). A good number of ironclads were also constructed or purchased from England. With the remaining being commissioned and put into operations by the CSA itself during the war. Interestingly, this also included some very early submarines, which is I think the first time they were used in warfare.

That said, the CSA was never able to effectively break the Union's naval blockades, and battles by the opposing armies were far more decisive in the war's outcome. Particularly in the strategically decisive Eastern Theater of the war.