I recently found out that my home states oath includes a denunciation against dueling and I was wondering how it fell out of fashion. http://www.lrc.state.ky.us/legresou/constitu/228.htm
Unfortunately you posted this just as I was turning in for the night, but I have written about dueling, and its decline, before. This would be the most comprehensive, discussing the decline in one of the follow ups Hope that helps, and happy to answer any follow-ups tomorrow!