Following the exhaustion of the so called “open regionalism” and in the midst of the social crisis generated by the application of the “Washington Consensus” formulas, the South American region has started to refocus its integration efforts over new axes and concepts. The new proposals are based upon the critical examination of the previous scheme, formed by what some have started to call “post-liberal regionalism.” The Union of South American Nations (Unasur), is the clearest expression of this change in tendency in the south part of the continent. The present study centers in displaying and understanding the background of this process; studying, in the light of the theories about regional integration and regionalism, both the forces that determine its dynamic and its conflicts and limitations. When assessing the convergence and divergence among its key players (the governments that lead the process), the analysis points to decipher the answers and scenarios of the new integration mechanism against the juncture, particularly, the ones generated by the U.S. foreign policy as well as the one originate by the socioeconomic and political restrictions within the region. Similarly, as a conclusion, carry out a provisional balance of the advancements and explore the possibilities, challenges and obstacles existing on the way of this South-American integration project.