In 1846, the United States was involved in the Mexican-American War, which began over territorial disputes following the annexation of Texas. This conflict led to significant territorial gains for the U.S., including present-day California and New Mexico. Additionally, 1846 marked the beginning of the Oregon Trail migration, as thousands of settlers moved westward in search of land and opportunity. This journey was crucial in shaping the westward expansion of the United States and the settlement of the Oregon Territory.