Watching a program on Volcanic Erupotions specificaly Krakatoa.
It gives info that, floods will result, tsunami's, earthquakes, nuclear winters, acid rain, floods and poison gas clouds and head waves and blast waves.
And all of those would result in:
1.) Death in so many levels which means bodies which will not be burried which means disease of so many levels which will turn into plagues.
Plague, cholera, typhoid and a host of other nastiness.
2.) Destroyed Infrastructure: we are talking communications, some will have an EMP effect, others will just make the com networks to disapear, and others well without power or maintenance they will stop.
Roads will be destroyed, bridges, ports, air travel, water pumps, stations and networks and purification plants. Damns which provide water, power and controlling water so we do not have floods and can navigate water routes gone!
Transport networks via road, rail, sea and air bringing in food, water and medical supplies gone and severely diminished!
Areas where oil is pumped and fuel is produced gone! Or severely diminished. If the oil is not produced inland and the refineries in similiar places it no longer exists! And the pumps at sea and coastal areas that will have flooded or at sea will continue to have oil flow <like in the Gulf of Mexico right now> And thus, a coat of oil or tar will cover large areas of our coastal regions, making it impossible for birds, fish or vegetation to live in those areas as well.
3.) Famine, nuclear winter, tidal waves polutted water, destroyed fishing grounds. A disruption in the natural cycle to include the seasonal patterns, wind and current patterns. Coupled with acid rain, pollutants of all maner from our factories and cities further poisoning region arround cities, factories, oil production and transport and storage networks.
4.) Cooling of the earth! A dramatic change in weather of the earth! Again the dying of plants, which means no food for the plant eating animals.
5.) Poison Gas and acid rains, polutting water sources, soil and other areas wherever the wind may carry them.
Those are some pretty stark events.
And then of course the regular damage the natural things will cause. Floods, Tidal Waves, Heavy Rains <as a result of the cooling, which will lead to ice storms and snowing>
All of this damage will cause a shortage of people to do work. It will also lead to war over remaining resources and farmland that is still workable, as well as potable water supplies.
All of the above is good material for using as material for a wicked campaign.