The document discusses three key factors that opened up the American West to migration in the late 19th century: the end of the Indian Wars in 1885, which eliminated a threat to settlers' safety; the invention of barbed wire in 1874, which allowed for fencing of open land and the end of cattle drives; and the expansion of the railroad network throughout the West in the late 1860s and 1870s, which made traveling and transporting goods much easier. These factors helped spark a mass migration to the West and rapid population growth in states like California in the late 1800s.