I feel like I should say something having done an AAR as the USA in KR.
First, you shouldn't have to abandon anything to the rebels in the 2nd ACW, or scrap your navy. If you play your cards right, you can win quite handily.
First, as soon as the game begins, set all of your IC to consumer goods. Your dissent will evaporate quite quickly if you do so, and by approximately May your dissent should be gone. One advantage you get as the USA is that while you pump all of your IC into consumer goods, countries like the Latin American ones will trade you supplies for natural resources. This can allow you to literally leave your IC allocation in supplies to 0, so you can focus on other matters.
Next, as soon as your dissent is on 0, put all of the extra IC you can into building infantry divisions. IIRC with about 6 serial runs of 3 to 4 infantry each, you should be able to form a decent core of regular infantry divisions to fight in the civil war. You should also be able to spare some IC to build some very cheap garrison divisions, which you can use to hold Washington DC.
Now, remember to choose carefully what choices you decide to make with the events leading up to the breakout of the 2nd ACW. Your choices can determine which states will break away from the Union and join the rebels. If you take a more hardline approach, like choosing MacArthur to form a military junta, the rebels will gain lots of support and can expand to include states like Virginia, Texas, etc, at least for the AUS. Try to take a more moderate path by letting the elections go forward and choosing someone like Garner under the democrats or whatshisface under the republicans (cant remember who the republican candidate was, i think it was Wendell Wilkie or something). If you make the right event choices, your dissent hits will not be very heavy and you will retain control over many important territories.
As for the war itself: Hit the CSA. Make sure you cover all of your borders, but concentrate your primary efforts on the CSA due to their industrial and military potential. In the west, you can hold the rocky mountains with nothing more than some infantry and militia dug into the rocky mountains. PSA forces should take a long time to mobilize, so they will not be that big a threat. The AUS will push hard, and can be a real challenge, but they are not invincible. If you have enough regular infantry, you should be able to contain any offensive by their large numbers of militias. As for the CSA, just cut them in two by going for Ohio. You will cut off all CSA forces in the east that way, and can easily crush them with little efforts after their supplies and org run out. When you are ready, move in for the kill, take Chicago, and the CSA will surrender.
Remember, when you defeat one of the civil war factions as the USA, you inherit their MP, build ques, and you gain control of all of their troops, airplanes, and warships. After defeating the CSA, New England should join the war on your side as well. With CSA industries, MP, and the remnants of their forces, you should be able to easily roll over and crush the remaining factions. Do to the AUS what the Union did to the Confederacy in the 1st Civil War and crush them with greater military production and numbers. The PSA may be a tougher nut to crack, but they will go in a similar way.
After all of that, you win.
