Natural
The desertification of North Africa is largely ascribed to over-farming of wheat by the Romans. Worked by slaves, they fed the legions, guards, patrols, builders, judges, and such, that formed the sometimes unwanted service economy that was overlaid on a population almost entirely composed of farmers.
This view is frequently cited in energy economics and green economics which note that the complexity of society requires more energy subsidy, in both food and fuel form, that leads directly to such effects as deforestation (wood being the dominant fuel of the Roman Empire).
Effects on modern politics
Rome is often cited as both a good and bad example by modern academics and politicians.
This is so self-serving as to be beneath comment in an encyclopedia, except to note how they do it above.
See also