Immigration has long been a hot issue in California, even as far back as the days of California's Mexican period (1822 to 1846). Then, as increasing numbers of American immigrants flowed without permission into the Mexican province of Alta California (all of today's California, Nevada, and Utah and parts of today's Arizona, New Mexico, Colorado and Wyoming), local authorities were alarmed. As described in a History News Network interview with UCLA historian, Dr. Steve Aron, Americans were considered dangerous because they were well-armed, failed to assimilate, refused to learn Spanish, and even brazenly flaunted their foreign flag. About 1846, the last governor of Mexican California, Don Pio Pico, lamented to California's leaders:
"We find ourselves suddenly threatened by hordes of Yankee [American] emigrants, who have already begun to flood into our country and whose progress we cannot arrest….Shall we remain supine while these daring strangers are overrunning our fertile plains and gradually outnumbering and displacing us? Shall these incursions go on unchecked, until we shall become strangers in our own land? We cannot successfully oppose them by our own unaided power; and the swelling tide of immigration renders the odds against us more formidable every day."
-- From A Tour of Duty in California (p. 24), by Joseph Warren Revere, Lieutenant, U.S. Navy, 1849.