I have severe doubts the U.S. would actually kick off a gigantic war for oil out of the blue; it's a democratic republic, you need popular support for a massive undertaking like this. Texas can be a very inhospitable region for military operations, and the South controls the relevant reaches of the Mississippi River; the U.S. would want to base its operations off a river or off the sea, which is by no means a sure thing when the Royal Navy has a say in things.
Plus, if the Europeans do want to get involved, it's not like in crackpot Nazi invasion TLs where they have to make an amphibious landing; the British still have Canada as a base of operations, and the U.S. can't invade Canada and overwhelm the Confederacy, not when they've had the chance to prepare themselves for years with forts and peacetime conscription and whatnot.
That's also discounting the very real possibility of detente between the USA and CSA; the two would doubtless become massive trading partners in the years following normalized relations; the war would likely end because of popular opposition to conscription and emancipation, the two things most necessary as means and motivation to make war on the Confederates again. If the war failed, the Republicans could be completely discredited; the northern democrats would use their political control to shore up their position by bringing in as many immigrants as possible and ensure a steady voting base, strengthen their political machines, take control of the important offices, etc.
Plus, if the Europeans do want to get involved, it's not like in crackpot Nazi invasion TLs where they have to make an amphibious landing; the British still have Canada as a base of operations, and the U.S. can't invade Canada and overwhelm the Confederacy, not when they've had the chance to prepare themselves for years with forts and peacetime conscription and whatnot.
That's also discounting the very real possibility of detente between the USA and CSA; the two would doubtless become massive trading partners in the years following normalized relations; the war would likely end because of popular opposition to conscription and emancipation, the two things most necessary as means and motivation to make war on the Confederates again. If the war failed, the Republicans could be completely discredited; the northern democrats would use their political control to shore up their position by bringing in as many immigrants as possible and ensure a steady voting base, strengthen their political machines, take control of the important offices, etc.