The document discusses three key factors that opened up the American West to migration in the late 19th century: 1) The end of the Indian Wars in 1885 marked by Geronimo's surrender, removing the threat to settlers; 2) The invention of barbed wire in 1874, which allowed for fencing of the Great Plains and ended cattle drives; 3) The building of transcontinental railroads under the Pacific Railway Act of 1862 and Land Grant System, which connected the West and greatly increased settlement.