The issue of development of defence systems gives a hard time to strategy developers in the countries with various level of economic, technological, social, and political development, same as to the academic and professional researchers and the individuals who implement those strategies. The challenges in front of them are more present than before, as besides political issues, many categories are influencing national security strategies' and defence strategies' development, such as technology development, economic crises, political influence, and social changes. This paper researches current literature on national security and defence strategies development and the most significant challenges that influence the development of national security strategy and defence strategy of the Republic of Serbia. In the second part, based on acknowledged challenges, the most important ones are discussed in the form of interviews with defence and security experts and academics, strategic management higher education teachers and the professionals in the field of defence, security, and information technologies. The paper concludes that the challenges are wide-ranging and are of various levels of significance. Nevertheless, the most important challenges that emerged are: demography (human resources) and education; risk management policies and procedures; cyber war, cybercrime, and cyber terrorism; economic crises and defence budgets; public health and global health crises; and climate change. Moreover, the interviewees singled out as the crucial category: the investment in education of human resources that would be capable of developing national security and defence strategies.