This thesis is a study of the norms and values of political culture during the 15th century.  The political culture gives the struggle for power in the Kalmar Union in the 15th century its characteristics.  The aim of this study is to identify the political culture and how it contributed to the political polarisation and disagreement within the Kalmar Union during the reign of King Karl Knutsson (Bonde) 1448-1470 and Regent Sten Sture 1470-1503. The theoretic approach is based partly on Eva Österberg’s definition of political culture, but mainly the theory is based on Harald Gustafsson’s thoughts and identified eight arguments for legitimising power used in political correspondence during the 16th century. These arguments are examples of how someone could express themselves to legitimise their power. The method used in this study identifies what non-vocal structures and values that are expressed in the official material of legal documents including treaties and open letters to or from the common people. Firstly, the context of the document is identified and information like who wrote it, when and why, secondly the study analyses how the operators’ addresses and use titles to one another. Thirdly the study identifies words and phrases that express positive values for legitimation. The values that has been found have been analysed in comparison to the law in order to identify if the values could be found in the laws as well. To conclude the study found that there are differences in how the operators expresses themselves and the emotional connection to the situation, although non-vocal structures like norms enforce the operators to apply a certain amount of respect. The political culture and the diplomatic mission creates the standards used in addressing their opponent. Therefore the choices of words are important and the study identifies five larger values that comes to light, they are law and justice, unity, assurances, commitments and duties and good characteristics. All of these can be identified during the entire research period and supported by the values expressed in the law.