the journey was taken by about 70,000 people beginning with advance parties sent out by church leaders in march 1846 after the 1844 martyrdom of the church's leader joseph smith made it clear that the group could not remain in nauvoo, illinoiswhich the church had recently purchased, improved, renamed, and developed because of the missouri mormon war, setting off the illinois mormon war. the well-organized wagon train migration began in earnest in april 1847, and the period (including the flight from missouri in 1838 to nauvoo), known as the "mormon exodus" is, by convention among social scientists, traditionally assumed to have ended with the completion of the first transcontinental railroad in 1869. not everyone could afford to transport a family by railroad, and the transcontinental railroad network only serviced limited main routes, so wagon train migrations to the far west continued sporadically until the 20th century.