Colonial California refers to the period when California was part of the Spanish Empire, primarily from the late 18th century to the early 19th century. During this time, Spanish explorers and missionaries, such as Junípero Serra, established a series of missions along the California coast, aiming to convert Native Americans to Christianity and promote agriculture. The Spanish colonial government also set up presidios, or military forts, to protect these missions and settlements. This era laid the foundation for California's cultural and agricultural development, influencing its future as part of the United States after the Mexican-American War in 1848.