I'm currently working on a timeline (which may be an exercise in futility) that's yet another one of those Balkanized U.S. scenarios, but meant to be in a pulpy tone. So I'm trying to reduce butterflies by having the Civil War begin as in OTL (with the election of a President Lincoln), yet Texas is an independent country.
But that doesn't work, does it? Without Texas, the U.S.'s slave-free state ratio is irrevocably modified, and so are the political fights surrounding that ratio. Furthermore, if Texas decides to go it alone, that sets a precedence that may lead the California Republic, the
Oregon Lyceum guys, and/or Mormons to declare their own independent country, since joining the U.S. becomes a less than obligatory thing. Not to mention the U.S.-Mexican War will probably go differently without the U.S. annexation of Texas, anyway.
However, suppose that this is a low-butterflies zone, and Texas is not in the C.S.A. Maybe the rest of the West is, maybe it isn't. Either way, how does this change the Civil War? If the U.S. doesn't stretch from the Atlantic to the Pacific at the beginning of the war, does this change perceptions of the Union? Would they fight more fiercely to retain the smaller amount of territory they have?