Why are the some of the people in manifest destiny picture looking back?

"The painting serves as an allegory for Manifest Destiny and American westward expansion. ... The figure of Progress is ushering an era of modernization, development, and advancement to the West, which in the painting is portrayed as a dark and savage place, especially when compared to the eastern side of the painting."

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workers of lowell mills were greatly benefited for the waltham type of work which was more a paternalist kind, trying to protect the integrity of this little girls coming from small farmers and providing an adequate place of work, this in an effort to avoid the issues of bad place conditions and immorality that the people in bigger industrialized cities of great britain were experimenting.

do you have a list of sources to choose from?