Western expansion refers to the period in the 19th century when the United States grew its territory westward. This movement was driven by the belief in Manifest Destiny, the idea that Americans were destined to expand across the continent. Key events during this time included the Louisiana Purchase, the California Gold Rush, and the establishment of the Oregon Trail. As settlers moved west, they faced challenges such as conflicts with Native American tribes, harsh weather, and difficult terrain. The expansion led to the establishment of new states and territories, significantly shaping the cultural and economic landscape of the United States.