San Diego is located on the site of the first European settlement in California. Juan Rodríguez Cabrillo sailed into San Diego Bay in 1542 and claimed the land for Spain. In 1769, Junípero Serra, a Franciscan missionary, established Mission San Diego de Alcalá and dedicated the Presidio, the first Spanish fort in California. By 1830, most of the people were living in what is now Old Town. It was under Mexican jurisdiction from 1822, when Mexico won independence from Spain, until 1846, when it was captured by a U.S. naval force. The city's population surged when the Santa Fe Railroad arrived in 1884.
San Diego became an important U.S. naval base during World War I; later, other branches of the military established bases here. In the 1950s, this concentration of military installations gave rise to San Diego's aerospace industry. The diversification of San Diego's economic base in the latter part of the 20th century contributed to its rapid growth. An urban revitalization effort began downtown in the 1980s starting with Horton Plaza, an expansive shopping mall that won acclaim for its dramatic architecture, as well as the inauguration of a trolley system. Other regional world-class attractions followed.
Today San Diego is the second-largest city in California and the eighth largest in the United States with a citywide population of 1.3 million residents and more than 3 million residents countywide. San Diego is not only a premier tourist destination, but an established leader in core industry sectors such as biotechnology, communications and software development. The city's prominence on the harbor and access to Pacific Rim countries has also established downtown San Diego as a hub of international commerce and the urban heart for residents and visitors alike.