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 illegally flowed into the Mexican province of Alta California (all of or parts of today's California, Nevada, Arizona, Colorado, Utah, Wyoming and New Mexico), 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. The last governor of Mexican California, Don Pio Pico, lamented to California's leaders of the time:
"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."