Gold had not been discovered there yet, but Polk wanted California and its magnificent San Francisco Bay as the American gateway to trade with China and other Asian nations. Polk was worried that other nations, such as England or France, might take California if the United States did not act.
Drawn by the Willamette Valley and its vast resources, settlers moved west to the Oregon territory (U.S.). President James K. Polk made it his goal to enforce manifest destiny, no matter what the cost. He told the British the Oregon Territory would not be shared and this ultimately led to the Pig War (U.S.).