Planning of development of energy systems today becomes closely connected to analysis of day-ahead energy markets, market coupling and dynamics of integration of both, renewable energy sources and demand response technologies. A common European energy market would enable larger integration of renewable energy sources but would also influence economic feasibility of new investments in energy production units, depending on the resources available and transmission available for import or export of energy from each market zone. In this research, methods are proposed for analysis of costs of production, storage and demand response technologies, organized in steps of energy transition in the surrounding zones; and use of game theory in assessing the long-term strategic decisions of market coupled zones. Objectives of this research are 1) To prove the value of the use of game theory in assessing the long-term strategic decisions of market coupled zones; 2) To demonstrate the need to include the influence of market coupled countries' energy strategy on national energy strategy; 3) To analyze the influence of integration of demand response technologies in coupled market zones on the feasibility of strategic decisions in the investigated zone. The hypothesis of this research is that optimal decisions in long term energy planning for each market coupled with neighboring zones can be determined by game theory, through achieving Nash equilibrium with energy strategies of surrounding zones, even in the case of lack of information about them. Results of five published scientific papers bring forward two major scientific contributions: A method for analysis of costs of production, storage and demand response technologies, organized in steps of energy transition in the zones surrounding the zone of interest is elaborated in PAPER 1, PAPER 2 and PAPER 3, providing methodological development of approaches for a single zone and for the interconnected group of zones, which defines outputs for electricity generation technologies, energy storage and demand response in technical context and in the context of economic assessment. The second major contribution is a method which provides robust assessment of strategic decisions using game theory, which can be a new standard for national energy planning. This contribution is realized based on the groundwork done in PAPER 1, PAPER 2 and PAPER 3, through the method developed in PAPER 4 and completed using the game theory in PAPER 5. The outcome of this research is a new method, which can be proposed as a standard for energy planning of the market zones, which are mostly national energy systems. The hypothesis of this research has been confirmed: optimal decisions in long term energy planning for each market coupled with neighboring zones can be determined by game theory, through achieving Nash equilibrium with energy strategies of surrounding zones, even in the case of lack of information about them - this is achieved through establishing a matrix of possible choices for all the zones included in the consideration and then using the proposed approach to calculate the payoffs of the choices and the developed game to reach a Nash equilibrium or the mixed strategy.