Traditional global models address important global problems using highly aggregated measures, but it may be argued that the world is strongly non-homogeneous at least at some fundamental level: developing (South) nations and developed (North) nations may have very different, asymmetric problems, goals and structures. This study aims to investigate these two distinct groups of economies in a context of global sustainability. We identified population, economic growth, welfare gap, energy supply and pollution as key issues and analyzed them in a systems perspective. A dynamic feedback model, which discriminates these two groups of nations, is constructed based on WORLD-3 model in order to study the dynamics of key parameters related to these issues for the period 1975-2050. Simulation experiments reveal that population characteristics of South and current mode of economic activity, which is extensively dependent on non-renewable energy resources constitute serious obstacles for the sustainability of the system. Hence, stabilizing the population growth in South, transition to alternative energy resources and investment support to South for this transition are vital for closing the welfare gap between blocks and sustaining the global system.