The following is a Capstone paper about Fort Worth Sister Cities International in Fort Worth, Texas USA and its sister city relationship with Nagaoka, Japan. The central focus is on citizen-to-citizen diplomacy and how much such diplomacy has contributed to peace between Japan and the U.S. overall in the post World War II era. Research Question: How have the Fort Worth-Nagaoka City Sister City exchanges contributed to peace building between the U.S. and Japan after World War II? Research Methods: The research methods used are questionnaire distribution by postal mail, interviews of high-level administrators, and a review of articles from secondary sources that have relevance to the research question regarding citizen diplomacy. The questionnaires were distributed to certain groups with affiliations with Fort Worth Sister Cities International and to Nagaoka and to the local community of Fort Worth who may not have any affiliation with Fort Worth or Nagaoka sister cities. This was done to lessen the chance of bias towards or against the effectiveness of citizen diplomacy in the answers provided and to gain information that would be relevant to the research question. As for the secondary sources, relevant articles were selected along with works on how to do research. Conclusions: Evidence from the research supports the research question in that citizen diplomacy has had a positive impact towards bringing peaceful relations with Japan. It is an effort with much long-term benefits towards preventing future wars with nations.