After suffering a humiliating defeat at the hands of the Texians in the Texas Revolution, Mexico attempted to increase central control over its states once again. Lack of confidence in the central government saw the establishment of the Republic of the Rio Grande in 1840. With negotiations for admission into the United States going nowhere, Texas instead decided to assist the Rio Grande's War for Independence. A third front opened for Mexico in the form of the Republic of Yucatan, and the three rebelling nations opted to form an alliance against Mexico, eventually forcing Mexico to capitulate in 1843.
Mexico officially abandoned California and New Mexico in the mid 1840s, with rebellions in Central Mexico becoming the country's main concern. Concerned that Britain or America would move into their backyard, the Alliance began working with the Californios of San Francisco Bay to establish a Californian Republic, which quickly became a signatory of the growing entente.
By the 1850s, Mexico had all but collapsed and the four allied Republics were approaching an ever-closer union. This finally came after William Walker managed to seize Baja California and Sonora from the downtrodden Mexico, petitioning Texas, Rio Grande, Yucatan and California to join his Republic of Sonora in a Confederación del Norte--a Confederation of the North. The Republics would remain functionally the same, but international relations and defense would be handled on a Confederal basis. The Articles of Confederation, a nod to the American founding document of the same name, were signed by the Presidents of each Republic on the 28th of October, 1853.
While all this had been going on, a large population of Mormons from the United States had made their way into what had been a sort of no-mans land in far-eastern California. Not concerned with anything beyond the Sierras, and Texas not especially bothered by the goings-on past the Rio Grande (the river), California quickly let the Mormons gobble up much of the desert beyond the mountains, creating the Republic of Deseret within the Confederation's borders. Concerned that another large Republic would tip the balance of power even more, Rio Grande demanded that Deseret be restricted to the land north of the Colorado RIver, instead suggesting that everything south of it be declared the Republic of Colorado. The Mormons were disappointed, but accepted the terms. Two new Republics would be added to the Confederation.
Chihuahua became the first territory of the Confederation in the mid 1850s, surrounded on 3 sides by the CDN and with Mexico undergoing rebellion every few months, representatives from Chihuahua aceded to Confederation rule.
The Oregon territory was actually a deal between Britain and the CDN. Negotiations as to the ownership of the Oregon Territory between the United Kingdom and the United States had almost reached the boiling point when the Civil War broke out in the late 1850s in the United States. Britain occupied the entire territory, but only desired the region north of the Vancouver River. They sold the rest to the CDN in 1859.
Love this, but I doubt Deseret would occur in this timeline as the Mormons didn't really want to flee to another nation. If the Deseret Plan happens in this timeline, I'd expect it to occur in modern day Idaho. The area here that is Deseret would most likely belong to California.
Yeah, that's probably more realistic. A lot of people in the Confederation at that point probably considered themselves American, though. Texas itself was less than 20 years old. They hadn't had much time to develop a national identity.
Think of it as more of the Austria to America's Germany. They may very well end up uniting in the end.