Halperin, M. H., Siegle, J. T. & Weinstein, M. M. The Democracy Advantage: How Democracies Promote Prosperity and Peace.
Accesat în 22 octombrie 2017.  ^ Halperin, M. H., Siegle, J. T. & Weinstein, M. M. The Democracy Advantage: How Democracies Promote Prosperity and Peace.