Thought of the acquisition of California by the United States dates back at least to the time of President Andrew Jackson. Under President Tyler, acquisition by purchase was actively considered. Upon the collapse of the Mexican Empire in 1824, which was followed by the Mexican Republic, President Polk entered upon his administration in 1835 with the definite resolution of winning the prize, offering to purchase northern California, including San Francisco Bay. His offer was refused. Yet, the slight tenure by which Mexico held California is clearly perceived –with some of the leading Californians even ready to welcome a change of flags.
Mexico's relations with the United States had become increasingly critical, largely because of the complex Texas question. California had come to be looked upon as a capital prize, sure to fall, in the course of a short period of time.
In an era of "Manifest Destiny," Colonel John C. Fremont is considered by some to be the actual conqueror of the California region in 1846. Encouraged, if not directly aided by Fremont, settlers at Sonoma, revolted against Mexican authority and on June 14, 1846, raised the Bear Flag, issued a proclamation declaring California to be free and independent.
