Part three of the case study series.
I submit the following for review.
What single element could destroy the world?
About world building? Insofar as destroying worlds is about world building yes, I believe this is on topic. My major gripe with this question was actually some of the answers it attracted. Many of the answers failed to take the premise of a mad scientist into account. This led to some modifications of the restrictions that I placed around the situation. I didn't feel that some of them should have been necessary but if you're not specific around here people tend to go for outlandish.
No, this question seems pretty strait forward on topic to me. If anything you could probably claim it is idea generation but I think the restrictions put in place make it clear I am looking for someone with chemistry/physics knowledge to fill in the gaps.
How would space battles alter combat tactics?
About world building? This question helps define combat in space, so in my mind is a discussion of how things differ from the combat we are used to today. Feels pretty on-topic, discussion of a system and how it impacts the world.
Risking off-topic? Nope, I am happy this one is well within scope.
What are the primary triggers for the decline and fall of great empires?
About world building? Yes this is about world building, specifically developing a history for the world in question.
Risking off-topic? I think it is probably too broad. We went back and forth on this question several times. It was an early question on the site so I can't recall exactly, but I think it was closed once or twice. This question would probably have benefited from the sandbox but I don't think it had been created yet. It could probably be reworked to be more on topic, I'm just not sure how.
How would multi-race humanoid evolution happen?
About world building? Absolutely.
Risking off-topic? Not at all. This one is nice and clean.
How to explain the co-existence of peace and violence in religion
About world building? Yes, the goal of this question was to help illuminate how this process works so it can be included in the world as a source of conflict throughout history etc.
Risking off-topic? It feels on topic to me but there could be an argument that this is a plot idea. I think the question is effectively framed as looking at the system though so it should be good.