Accounts differ about the rape of white women captives. This practice was common among the western Plains Indians, but many accounts (including Teddy Roosevelt's account of those times) claim that the Eastern Indians believed that rape of captives would lessen the fighting essence that they had cultivated through rituals in preparation for war. However, other accounts say rape of white female captives was common among the Eastern Indians also, but the accounts were oppressed due to public squeamishness in discussing the issue.
The bottom line is, Americans could not have expanded throughout the interior of the US, unless the Indians were tamed (ie, the Indian attacks had to cease).
You may wish to listen to Mrs. Flora Robertson talking about Oklahoma. Warning :-Contains negative stereotypes of Native Americans at the American memory project.
http://memory.loc.gov/cgi-bin/query/r?ammem/toddbib:@field(DOCID%2B@lit(4119b1))