Beginning in the 1920s, there was a strong movement in the United States (and not just in North Carolina) towards forced sterilization for eugenic purposes. The major goal of this was to "improve" the American gene pool by making it impossible for people who were judged inferior in some way to procreate.
The eugenics movement felt that many social problems would be greatly reduced if certain kinds of people were sterilized. They wanted to sterilize those with low IQs or those who tended to engage in "antisocial" behavior. For example, some women who were deemed to have bad sexual morals were sterilized. The whole purpose of this was to try to ensure that such traits (which were believed to be genetic) would not be passed down. This would improve the gene pool and would prevent the state from having to spend so much on things like programs for the poor.
North Carolina shared these concerns. It is unique mainly because its eugenics program continued long after other states had abandoned theirs.