1803: Louisiana Purchase doubles the size of the United States.
1823: Congress designates all navigable waters (rivers and canals) be post roads.
1832: First mail is carried by train.
1838: Congress designates all railroads as post roads.
1845: Congress creates star routes. This allows contractors, like stagecoach and Pony Express companies, to move the mail.
1846: The U.S. acquires the Oregon Territory.
1847: U.S. postage stamps issued meaning payment to mail a letter could be made by the sender.
1848: The U.S. acquires California and additional territories from Mexican Cession.
1848: Gold discovered in California.
1855: Pre-payment of mail became required, meaning payment to mail a letter had to be made by the sender.
1860: Pony Express Service started bringing mail between California and Missouri. It lasted 18 months.
1861: The American Civil War begins.
1863: Postage rates become uniform, regardless of distance.
1864: Railway mail service begins; for the first time, mail is sorted on-board the train.
1867: The U.S. acquires the Alaskan Territory.
1869: Cross-country railroad completed; now mail can travel from coast to coast in 3 days.