The country grew quickly and by the 19th century land in the settled areas was no longer cheap. There was a limit to how many times a father could subdivide his land among his children to give them a plot of their own, so more and more children had to leave the family home in order to make a living. Some of them went to the cities to find work, and others moved west where cheap land was available.
In the early 1800's, much of the travel to the west was on trails like the "Cumberland Road," later called the "National Road," which funneled early pioneers into the midwest. In the early- to mid-1800's, pioneers began to travel farther west on the Oregon Trail, the Santa Fe Trail, and other major wagon train routes. By the middle of the century, the railroads were beginning to make travel easier, and in 1869 the transcontinental railroad was completed, making it possible to ride coast to coast in comparative comfort on a train.
Railroads encouraged the use of their new western lines by offering to sell land to potential settlers at low prices, over long terms, and at low rates of interest. Later, the federal government decided to further encourage the development of all the western states and territories by enacting the Homestead Act of 1862. The Homestead Act declared that any citizen or intended citizen could claim 160 acres of unoccupied public land in "public domain states," virtually any part of the country outside the original 13 colonies, Tennessee, Kentucky, Texas, and Hawaii. Claimants had to improve the plot with a dwelling, grow crops on it, and live there for five years. If the original filer met these requirements and was still on the land five years later, it was his property, free and clear. The opportunity to get free or low cost land drew millions of people out to the west, including many of the new immigrants pouring in from Europe and other parts of the world.
In 1800, the largest cities in the country were all in the original 13 colonies. By 1850, some of the "gateways" to the West, like Cincinnati, St. Louis, and New Orleans, overtook the eastern cities as the largest cities in the country. By 1900, the Midwest had become quite settled and many of the largest cities in the country were in the Midwest. (Largest U.S. Cities) (Population Percentage by Region)
The westward migration of the country contributed to the dispersion of families. Although a few families took their elderly relatives along on the difficult journey west, a number of the western settlers left their parents and other relatives behind in the East. Some families made several moves, perhaps settling in the Midwest for a time before moving farther west. Each time they moved on, some members of the family might decide to stay put, leaving relatives scattered along the migration route. Over time, the massive westward migration made it less likely that many, or any, children lived near enough to their parents to provide help.