Not much is known of the very early history of Cavalier County. The Sioux are believed to have been the earliest residents, and the first known white men to enter the county were members of the Verendrye expedition, which camped in the Olga area in November 1738. In the 1790s, Chippewa from Minnesota and the Great Lakes area moved into the North Dakota Plains for the fur trade after companies established posts along the Red River, but heavy Sioux attacks in 1798 forced them back to Minnesota. They returned two years later to trap along the Pembina and Red Rivers, and although Sioux attacks increased and led fur trade companies to withdraw in 1808, the Chippewa remained and continued trading. Fur trade activity then steadily declined despite a post established in Beaulieu in the early 1830s, and the conflict culminated in a large battle west of Olga in 1848 that most accounts portray as a Chippewa victory. Beaulieu later became a rendezvous for the Chippewa and the Metis, and as the Chippewa population and fur trade declined, the Metis began moving into what is now Cavalier County. They were served by a trail from Winnipeg to Fort Totten and Devils Lake, with trading posts at Olga and Beaulieu serving travelers, settlers, and likely Native American buffalo hunters. Cavalier County was created from the western part of Pembina County in 1873 and was named for Charles Cavileer, a fur trader, customs agent, and postmaster. Olga became the county's first officially established community in 1882, when a church and post office were built. The railroad then drove the county's development as settlers founded small communities in hopes of attracting the line. The Great Northern Railroad was built from Park River to Langdon in 1887 despite difficult coulees and ravines, and by 1897 its line ran through Union, Milton, Osnabrock, Easby, Langdon, Dresden, Wales, and ended in Hannah. Additional lines were completed in 1905 through Weaver, Munich, Clyde, Calvin, and Sarles, and from south of Nekoma through Loma, Alsen, and Calio, while a spur from Canada into Maida was built in 1918. These rail lines sustained nearby communities for many years by carrying supplies, mail, passengers, and later grain, while steam engines gave way in the mid-1930s to a diesel engine nicknamed the Galloping Goose, and daily passenger rail service ended on October 31, 1959. Settlement was also shaped by the Homestead Act of 1862, which allowed land claims through residence and improvement, Timber Culture patents, or pre-emption. Much of Cavalier County land was acquired this way, and because building materials were scarce before the railroad arrived, many early settlers lived in claim shacks or sod huts, with some families gaining additional land by combining a homestead claim with a Timber Culture filing.