San Diego, California, has a rich history dating back thousands of years. The area was originally inhabited by the Kumeyaay people before Spanish explorer Juan Rodriguez Cabrillo arrived in 1542. The city was later founded by Spanish settlers in 1769, and it became a part of Mexico in 1821. In 1848, following the Mexican-American War, San Diego became a part of the United States as a result of the Treaty of Guadalupe Hidalgo. The city experienced rapid growth during the Gold Rush of the 1850s and the completion of the transcontinental railroad in 1885. San Diego played a major role in World War II as a hub for the U.S. Navy and Marine Corps. After the war, the city saw a boom in population and development, becoming known for its military presence, aerospace industry, and tourism. Today, San Diego is a vibrant city known for its beautiful beaches, thriving economy, and diverse culture.