Causality - Read ch. 5 and 6 (Gerring Christenson book)
1) Define a class of events you would like to explain (define your Y)
For example: why some (otherwise comparable) countries spend more or less on defense?
2) Try to generate three alternative theories/explanations (use different frameworks - combinations allowed). You need to define the IV´s (conceptualize them and if needed provide a brief operationalization) + define the logic of your explanations.
So eventually, you will define the independent variable (or variables) and the general logic of a mechanism connecting IV and DV.
At least one explanation will use two IVs!
3) In the next step, construct the (simplified) counterfactual outputs for alternative values of your IVs. E.g. low X leads to high Y, low X leads to low Y. A 2x2 table could be useful here.
4) Try to find at least two actual empirical cases within the scope of your theory, measure (estimate) the IV´s and propose a hypothesis (regarding the value of your DV).
Compare "predictions" (hypothesized values) for your two cases with the actual situation (actual values on the DV).
5) Summarize your findings into a nice (read "J. Schwabishian") table + short text.
Your theories will have to be quite simple (naive if you want) unless you want to spend the next 30 hours on thorough research. If some data for your cases are missing, you can make "an expert estimate" (in that case, mention it).