For the Mexican government to go to war with its more powerful northern neighbor in 1846 was folly. Mexico surrendered to the United States more than half a million square miles of territory, contributing to a legacy of distrust and bitterness towards the U.S. that has never entirely dissipated. The real prize was California. The Californios—Spanish speaking, non-native inhabitants of the province of Alta (Upper) California—had ambiguous loyalties to the Mexican government and minimal military capabilities. American control of California was considered the keystone of Manifest Destiny, and naval and amphibious operations along the Pacific coast began as early as 1821 and continued for weeks after the end of the war. This book describes the often overlooked military and naval operations in California before and during the Mexican War, and introduces readers to the colorful Californios, the American adventurers who arrived after them, and the Indians, who preceded them both.