In the quantitative analysis of conflict, we have a variety of problems. One is that we tend to adopt a single variable as a principal focus of inquiry for an extended period of time. Over the years, contiguity, arms races, alliances, capability ratios, territorial issues, regime type, rivalries, economic interdependence – to name some of the foci of the past few decades – have sequentially preoccupied much of our attention. There is nothing wrong with an exclusive focus on certain arguments about how conflict comes about. Everything cannot be examined every time we do an empirical analysis. We probably need to develop very specific foci in order to determine what seems to work, as well as what does not seem to work. Still, there is a cost to very specific foci. We tend to either dismiss variables that do not seem to be working or lionize those that do seem to be providing some explanatory and predictive value. The obvious antidote is to at least occasionally avoid relatively narrow foci and try to bring together multiple perspectives simultaneously. But how best to do that?

Another problem is that our arguments tend to be fixed on specific variables. So we have arguments and theories about deterrence, capability, and/or democratic/liberal peace that suggest the utility of examining some variables but not others. By suggesting that we borrow a framework from analysts of disease, Russett (2003) offers an interesting vehicle for getting around this problem. Some factors induce disease while others suppress it.