1841: Oregon Trail - People begin to travel west in wagon trains on the Oregon Trail. Around 300,000 people would take the trail over the next 20 years. 1845: Manifest Destiny - Journalist John O'Sullivan first uses the term "Manifest Destiny" to describe the westward expansion of the United States. 1845: Texas becomes a U.S. State - The United States officially claims Texas as a state, eventually leading to the Mexican-American War. 1846: Brigham Young leads 5,000 Mormons to Utah - After experiencing religious persecution, the Mormons move to Salt Lake City, Utah. 1846-1848: The Mexican-American War - A war fought over the rights to Texas. After the war, the United States paid Mexico $15 million for land that would later become California, Texas, Arizona, Nevada, Utah, and parts of several other states. 1846: Oregon Treaty - England signs the Oregon Treaty handing over the Oregon Territory to the United States. 1848: Gold Rush begins - James Marshall discovers gold at Sutter's Mill. Soon word is out and people rush to California to strike it rich. 1849: Around 90,000 "Forty-niners" move to California to find gold. 1860: The Pony Express begins to deliver mail. 1861: The First Transcontinental Telegraph line is finished. The Pony Express shuts down. 1862: Pacific Railroad Act - The United States government agrees to help fund a railroad from California to Missouri. 1862: Homestead Act - The U.S. government offers up free land to farmers who agree to live on the land for five years and make improvements to the land. Many people rush to places like Oklahoma to claim their land.