The flags of three different nations fluttered over California during Juan Bautista Alvarado's life: Spain, Mexico and the United States. Alvarado was California's first civil governor and, with J. Neeley Johnson, the youngest at age 27. His biographer, Robert Miller, noted that the "study of Alvarado's life illuminates much of California's history during the Mexican period and the transition to American rule." In 1809, when Alvarado was born in Monterey, the capital of Alta California, the Spanish possession had a population of about 2,000 Spanish-speaking colonists. The Alvarado family lived in the presidio at Monterey. It was well-fortified with 5-foot-thick adobe walls standing 12 feet tall. Alvarado's grandparents came from two illustrious military families, the Alvarados and the Vallejos.