I haven't read any of Blattman's writings but in case I'm not too late and these aren't being covered, I'd be curious to hear his thoughts on

1. The impact of international institutions in regard to war (e.g., do they help prevent and/or end wars, are they merely an extension of power by different means, do these examples represent institutionalism and realism respectively which perhaps he thinks we should be "down with")
2. The impact of nuclear weapons on willingness to fight (do they, in his view, help prevent war)

For what it's worth, I took a course on Causes of War in college ~ten years back with Professor Gary Bass, and I still have the syllabus alongside a summary of a few of the assigned readings. It's raw, but if you're still looking for inspiration I'm happy to share them for you to skim.