Westward expansion refers to the period in the 19th century when the United States grew its territory westward across North America. This movement was driven by the belief in Manifest Destiny, the idea that Americans were destined to expand their land and influence. Key events included the Louisiana Purchase in 1803 and the California Gold Rush in 1849, which attracted many settlers seeking new opportunities. As settlers moved west, they encountered various challenges, including conflicts with Native American tribes and harsh environmental conditions. The construction of railroads, such as the Transcontinental Railroad, facilitated travel and trade, further promoting settlement in the western territories.