The question how Darwinian mechanisms lead to the evolution of individually costly cooperative behavior has given rise to a number of hypotheses. However, attempts to build a synthesis where different types of mechanisms coexist and interact at different levels of selections are still scarce. Here we derive simple game theoretical models where the group level conflicts are resolved by group selection while simultaneously within group competition is resolved by kin selection and reciprocity. We show that none of the mechanisms, when alone, is as robust in evolving and maintaining cooperation as a synthesis of all. Furthermore, we show that initially within group conflicts can be overcome only by kin selection and not reciprocity. However, once common, different types of reciprocities can maintain high levels of cooperation even if average relatedness among individuals is lowered, groups become large, and the benefits of cooperation are reduced. Based on the synthesis we also propose a possible route to the evolution of social and eusocial systems.