My memory isn't good enough to recall the name of the paper, however doing some searching I see the field has not stood still. Here[1] is an example of a more recent paper where they've included more variables. A quote from the conclusions:

The closest natural resource–society interaction to predict conflict risk according to our models was food production within its economic and demographic context, e.g., with GDP per capita, unemployment, infant mortality and youth bulge.

[1]: https://www.mdpi.com/2071-1050/12/16/6574 Revisiting the Contested Role of Natural Resources in Violent Conflict Risk through Machine Learning (Open Access)