San Diego ( SAN dee-AY-goh, Spanish: [san ˈdjeɣo]) is a city on the Pacific coast of Southern California, immediately adjacent to the Mexico–United States border. With a population of over 1.3 million residents, it is the eighth-most populous city in the United States and the second-most populous in the state of California, after Los Angeles. San Diego is the seat of San Diego County, which has a population of nearly 3.3 million people. It is known for its mild year-round Mediterranean climate, extensive beaches and parks, long association with the United States Navy, and recent emergence as a healthcare and biotechnology development center. Historically home to the Kumeyaay Native Americans, San Diego has been referred to as the Birthplace of California, as it was the first site visited and settled by Europeans on what is now the West Coast of the United States. Upon landing in San Diego Bay in 1542, Juan Rodríguez Cabrillo claimed the area for Spain, forming the basis for the settlement of Alta California 200 years later. The Presidio and Mission San Diego de Alcalá, founded in 1769, formed the first European settlement in what is now California. In 1821, San Diego became part of the newly declared Mexican Empire, which reformed as the First Mexican Republic two years later. California was conquered by the U.S. in 1848 following the Mexican–American War and was admitted as the 31st state in 1850. The largest sectors of the economy of San Diego include military and defense-related activities, tourism, international trade, research, and manufacturing. The city is home to several universities, including UC San Diego, San Diego State University, and the University of San Diego. San Diego is the economic center of the San Diego–Tijuana region, the second-most populous transborder metropolitan area in the Western Hemisphere, home to an estimated five million people as of 2022. The primary border crossing between San Diego and Tijuana, the San Ysidro Port of Entry, is the busiest international land border crossing in the world outside of Asia (fourth-busiest overall). San Diego International Airport is the busiest single-runway airport in the United States.