RMG said:
Possible POD: Texas never gets annexed?
Very close, Texas doesn't get annexed because of the POD.
I'm thinking something like this:
Calhoun (an ardent states' rightest) wins the election of 1826, and appoints S.C. judges. Andrew Jackson leaves for Texas (as did many failed politicians from Tennessee and Kentucky).
Clay is elected after Calhoun. The Nullification Crisis (or something very similar) happens, the South bolts about 1830, and the Supreme Court upholds their right to do so. GB also supports the South, so it becmes a fiat accompli.
Jackson, who is now in Texas, becomes involved in the Texas revolt. Although he was a populist, he also believed in a strong central govt., and as a result, after the Revolt, he and others decline to join the South, in favor of a robust central government.
In the 1850's there is a border war between the US and the South, largely won by the US, GB agains enters, but the price is they sell Western Canada to the US. Texas supports the US, but the US cedes Arkansas to Texas.
1840-47, political unrest in Europe, immigration increases, with Texas and the US basically 'bidding' for the immigrants to support either their territorial ambitions (Texas and the South West, or their industry).
1845 US emancipates slaves to appeal to European immigrants (Since slaves are a relatively small portion of the population this isn't hard anywhere except Maryland.)
California Republic forms pretty much right on schedule, but joins none of the others, and due to the balance of power and its gold is able to maintain its independence.
1855, Mexican War, Texas and California each take a chunk of Northern Mexico. Continued Texas expansion in to the West.
1865 Texas War with the Southern Compact is supported by the US because of its desire for access to the Gulf through Louisiana. Louisiana ceded to Texas. Southern Compact becomes a source of raw agricultural materials.
1865, California purchases Alaska from Russia.
1885, California and Texas support the succession of the Pacific Coast from the US, because of the growing strength of these two areas, US permits the succession after extracting certain key rights through the treaty, and joining Alaska to the new Republic. California is forced to agree.