There is a long literature stating that war contributed to state building. Here, for example, you can find a paper by Nicola Gennaioli (Bocconi) and Hans-Joachim Voth (Zurich). It argues that European states needed money to win wars. Thus, states got better at raising money or resigned themselves to irrelevance.
It a powerful thesis, so much that even Paul Collier alluded to the possibility that Africa might be better off if the post-1945 world allowed for violent border changes. Let Rwanda expand! In extremis, you might even want to create institutions (like the ones in the pre-1914 West) that would encourage cohesive states like Rwanda to expand.
Or perhaps not. Did war encourage state-building in Africa before the Europeans invaded? If so, then it might be true that the continent would be better off had that process been allowed to continue. If not, however, then the implication is that European conquest did not abort local state building ... and unless something has changed radically, there would be little reason to believe that allowing that process to restart today would result in anything other than more death and destruction.
Mark Dincecco (Michigan), James Fenske (Oxford), and Massimiliano Gaetano Onorato (IMT Lucca) have done the work. They coded up 1,750 conflicts in Africa, Asia, and Europe between 1400 and 1799. In Europe and Asia, more war in the past predicted stronger and richer states in the present. But not in Africa! In Africa, more war before 1799 has no effect on economic development today ... and is in fact associated with more civil war.
The result is strong and intriguing. Go read the paper! Africa is different. Past war does not improve present results on that continent. The unanswered question is why. Section 6, where they try to address that question, is the weakest part of the paper.