When Mexico gained its independence in 1821, in theory it also acquired control of California. However, Americans were already starting to arrive, despite the immense difficulty of getting to California - three months by sea via Cape Horn, or four months overland in a covered wagon. Though the non-native population was a mere ten thousand in 1846, the growing belief that it was the Manifest Destiny of the United States to cover the continent from coast to coast, evident in the aggressively imperial policies of President James K. Polk, soon led to the Mexican-American War . Virtually all the fighting took place in Texas; Monterey was captured by the US Navy without a shot being fired, and by January 1847 the Americans controlled the entire west coast. In 1850 California became the 31st US state.

By chance, a mere nine days before the signing of the treaty that ended the war, flakes of gold were discovered in the Sierra Nevada. Prospectors flooded west, in the most madcap migration in history; it took just fifteen years to pick the goldfields clean. The completion of the transcontinental railroad in 1869, built using Chinese laborers, was a major turning point. The crossing from New York now took just five days, and a railroad rate war brought fares down to as little as $1 for a one-way ticket.

California was perceived as immune to the worst effects of the Great Depression of the 1930s - thanks in part to the images of prosperity promulgated by its now-established film industry . From the Dust Bowl Midwest, entire families of " Okies " packed up everything they owned and set off for the farms of the Central Valley, though they often found bleak terrain and a hostile attitude to newcomers. Heavy industry came during World War II , in the form of shipyards and airplane factories, and many workers and military personnel stayed on afterwards.

As home to the Beats in the Fifties and the hippies in the Sixties, and a host of radical political and ecological movements since, California was at the cutting edge of cultural change. However, the illusions of the Flower Power days were shattered by the violence of the 1969 rock concert at Northern California's Altamont Speedway, and once the anti-Vietnam War struggle was over, popular culture seemed to withdraw into smug self-satisfaction. The junk-bond boom of the Eighties, however, crash-landed in a tangled mess of scandal, and for California the Nineties kicked off with a stagnant property market, rising unemployment, escalating gang violence and racial tensions in LA, and an appalling death toll from AIDS in San Francisco - compounded by earthquakes, drought and flooding . Yet despite all the problems, and with more-conservative Californians fleeing the state for more hospitable climes in Colorado and Arizona, at the turn of the millennium the state continues to attract countless new migrants from the rest of the US and the world, who continue to provide much of the economic growth and cultural vitality of this dynamic, ever-changing place.