This paper examines characteristics of relationship between state failure and armed group in both perspectives of state sovereignty and contemporary armed conflicts. This work is also related to pave a way for overcoming dilemmas on peacebuilding activities after uniting peace agreement for terminating armed conflicts. First of all, the author of this article tries to seek a distinction between the success and the failure by dating back to historical way for building state sovereignty. Secondly, this article attempts to grasp complexity on contemporary relationship between state failure and armed group. With surveying arguments both on state failure and armed group, the author of this article seeks a correlation between them with characteristics of the complexity. Finally, this paper attempts to show an implication for peacebuildng on the basis of the analysis in the previous sections. This paper concludes that challenges for peacebuildnig inevitably stick to the work for building state toward the success programmed the notion of state sovereignty, however, peacebuilders ought to overcome these difficulties according to the different structure of state failure, which the author of this article designates, at least.