California was first settled by Mexicans in the 1790s, however, within two generations, Mexico would be forced out and British settler would mix with the Mexicans. This eventually gave to Britain's most powerful dominion. British settlers mainly landed in Oregon, a place that would once become the Republic of Oregon. However, border disputes between Mexico and Britain were frequently explosive, which resulted in the Anglo-Mexican War of 1846. Although Mexico had a large army, while Britain's forces at first consisted of just irregulars, their supply lines were long and they were stretched thin as they had to fight both Oregon, the Mormon rebels in Utah-Nevada and Texas. The arrival of the regular British army in the summer of 1847, made Mexico's defeat inevitable. As part of the Peace of Seattle, Mexico was forced to surrender California, grant independence to Aztlan and Deseret, while withdrawing their border with Texas to the Rio Grande. Mexico never recovered, while Britain found itself with invaluable bases on the Pacific coast.
California enjoyed the benefits of a gold rush, bringing enormous wealth to the country. California allied with Britain during the Great War, enduring a Mormon invasion, which they threw back. It also aided Oregon in taking Hawaii, but it remained very much a junior partner in the naval struggle against Japan. However, it fought heavily against the Mormons and Mexico, including the grinding battles in the Imperial Valley and northern Baja California. After the war, California was the first of the major combatants to fully recover, although it did not escape the effects of the Great Depression. When, the Mormons invaded West Nevada (a strip of land taken from Deseret at the end of the Great War) and the Mexicans, the Imperial Valley, California was unprepared. The war was a brutal stalemate in the Imperial Valley, but the Mormons were a massive threat, nearly splitting the country in half, while causing massive damage to California's well planned infrastructure. However, they were beaten back again and Deseret surrendered again in 1946, becoming the last of the Entente to continue the war against the Quadruple Alliance. California gained the whole of Nevada and Baja California, reducing the power of Mexico and Deseret severely.
In the post war years, California and Japan clashed over the Hawiian Islands the other territories in the Pacific. This resulted in a series of regional, but violent conflicts between California or Japan, or their respective puppets. The most important were Mao Zedong's Chinese Rising, the Vietnam War (sparked by the Californian running of supplies to Mao's forces through their ally, North Vietnam) and the Korean War.