*Have Santa Anna die in battle at the Alamo
*Texas gains independence, gains British protection per OTL in 1841. Texas and Mexico continue arguments over Western Territories
*Oregon territory feud goes hot in 1848 and US loses after three years. All of Oregon goes to UK including claims to southern Alaska (61 degrees) along with half of Maine and the whole of the Louisiana Purchase west of the Continental Divide.
*Oklahoma forms as a truly native native American nation under British protection about the same time
*Mormon settlers move into Salt Lake Valley as news of gold discoveries in California reach Mexico City, which dispatches over a third of its small army to the area around San Francisco.
*American Civil War begins as per roughly OTL time, preventing any westward ambitions from taking root.
*Mexico avoids defaulting on debt via California gold, intervention by European powers is avoided. Conservative elements succeed in bringing about monarchy regardless with Maximillian I still becoming (Constitutional) Emperor and working *with* Benito Juarez.
*California attracts immigrants and Spanish-speaking population is quickly outnumbered. Pio Pico continues as able governor into 1880s.
*Mexican monarchy attracts additional investment and uses gold money to fund railways, industry, and agricultural development. By 1870 a railway connects San Francisco with Mexico City.
*Province of Deseret formed out of New Mexico, Mormon settlers push into southern Wellington (Idaho), southeastern Palmerston (Oregon), and northern Houston (Colorado).
*US begins to top out without further frontiers, its West remains fertile but poor farming territory while its east remains dependent on materials that often require importation. Appalachian mining becomes far more prolific and secured from interference as coal is a prime US export.
*Mexico initiates Panama Canal after French fail to finish it, subsequently annexes Panama. Cebtral America gradually restored to Mexican statehoods by legal, illegal, and military means.
*Mexican shipbuilding becomes a focus both for naval development and industrial planning, by 1900 they have the best tier 2 navy in the world and produce just under a tenth of the world's new merchant shipping. Crown Prince Karl marries Crown Princess of Brazil.
*Mexico aids Cuba and Puerto Rico against Spain in 1898 after the explosion of the Sonora in Havana harbor. Subsequently each becomes an autonomous province of Mexico while the Philippines are directly annexed. The Kingdom of Hawaii also grants Mexico basing privileges at Pearl Harbor as a way of retaining some measure of independence.
*Colombia and Mexico go to war over a dispute regarding Darien. Venezuela and Ecuador join Colombia, it's a near-draw but by 1907 Barranquilla becomes a Mexican enclave. US toys with joinings but wisely decides to stay out of it as its navy is still rebuilding.
*Cascadia is given independence by the UK in the same legislation that grants South Africa independence. Immediately a trade bloc begins to form which will grow to include Mexico, Texas, the US, Spain, Colombia, Venezuela, Brazil, and Ecuador.