Oh, how different history might have been if the south had won their independence...
If that had happened, it would only have been a matter of time before the west declared themselves their own seperate country. The Union might choose to press a fight over it, if only to get gold. Nobody really bothers to make Hawaii or Alaska a state. Eventually Texas eats the rest of the south. We never really get around to building the Panama canal, and trade between the pacific and atlantic oceans remains low. On the plus side the stock exchange doesn't crash, but that doesn't really matter because the dustbowl still occurs, causing the central states to practically be abandoned. The Manhattan project is never started because the 'americans' lack the resources to pull off such an intensive project. Before the government in California even knows what is happening San Fransisco has been bombed by the japanese. The West States are conquered in 1942. The Union does send some aid to england, but lacking the resources most of that aid is sunk by german U-boats. Alone in the fight with no real allies to turn to, England surrenders in 1943. The Germans complete their atomic bomb in 1946 and use it on Boston. The Federal government puts up a valient fight, but by 1952 most of the northern states are a wasteland. A few of the southern states choose to ally with the north to help them fight off the germans, but many are over in texas trying to hold back the japanese advance. By 1960 japan develops their own atomic weapon and declares war on germany. The ensuing nuclear exchange drives the world into nuclear winter, and everyone loses.
Now, aren't you glad the north won?