What major event accelerated the westward expansion to California in the mid-19th century?

The Gold Rush is the major event that significantly accelerated westward expansion to California in the mid-19th century. Beginning in 1848, when gold was discovered at Sutter's Mill, news of the find spread rapidly, leading to a massive influx of prospectors, settlers, and entrepreneurs from across the United States and the world. This surge of migration dramatically increased California's population and played a crucial role in its eventual statehood in 1850.

The excitement and promise of wealth in the goldfields not only drew individuals seeking fortune but also catalyzed improvements in transportation, such as the establishment of more efficient trails and railroads. This expansion of infrastructure facilitated further migration and economic development in the region. The Gold Rush transformed California into a land of opportunity, forever altering its demographic, cultural, and economic landscape.

While the California Mission System laid the groundwork for early European settlement and the Mexican-American War resulted in the United States acquiring California, it was the immediate allure of gold that propelled rapid expansion during this period. The Spanish-American War occurred much later and did not impact the westward movement to California.