The theme is put there to inspire you, not to hold you back. I have two C-III maps, Save the Forest and Woodstock, that refer directly to environmental issues. In both ones the scarcity of wood is a central feature.

You could do the same with water, or olives, or grapes. Make wolves an endangered species and forbid killing or pinning them down, restrict fishing, or only allow wheat, vegs and fruit for a strictly vegetarian diet. Just make up some story around it to blow it up to a global problem. One of the (remotely) possible causes suggested for the downfall of the Roman Empire was the use of lead in the glazing of pottery, so even that can be used.

So if you, or anyone else has an idea for a C-III map, by all means come forward, and we will find a way of fitting it into the theme, frankly I can't think of any scenario I cannot fit into.

Note that we will help you develop your scenario, and such help will in no way disqualify you for winning the contest, on the contrary I dare say. I will happily scratch your back, don't expect you to return the favour.