In some respects, the question answers itself. The idea of popular sovereignty is one whereby individuals resolve contentious issues through voting. The issue of slavery was not one that could be "voted away." Simply put, this means that for every vote in the North that was against slavery, there was another in the South that stood for it. In this, popular sovereignty was shown to be a failure because it could not bring resolution. It created a voting stalemate, or the idea of "squatter sovereignty," whereby individuals rushed to a particular area to vote their own beliefs, and in the process, completely undermining the idea of popular sovereignty. In the end, popular sovereignty was shown to be a failure because it demonstrated that there are some beliefs that cannot be democratically vitiated and minimized. There is intensity and passion attached to the issue of slavery, something that cannot be minimized through voting. It is because of this that popular sovereignty was shown to not be effective in minimizing the tensions and antagonisms that arose before the Civil War.