In my game I'm going to have an old kindom of to be discovered peice by peice that the town they live in lost contact with. Now I want the old kingdom to be suitably ruined. We're talking a province 300 miles n-s and 150 miles east-west so it's a large kingdom. Now there were a number of factors that caused it's downfall that the players will discover throughout the game (csi style). Here's the kicker. The town they live in has been out of touch with the old kingdom for about 16 years as of the end of the last chapter of this game. I was going to start the new game 4 years later. On to my question.
If the factors are severe enough, could a kingdom go from almost prosperity to ruin in 20 years? Say the decay started on the west southwest corner 25 years before the present. I know i'm being vague, but I don't want to give too much away in case my players check this LJ forum out.
Basically, what degree of ruin could one expect after 20-25 years? Describe the condition of cities, outlying farms etc. as you would logically picture them. Imagine most of the damage done was done through warfare, violence and disease, starvation and depression.
If you do not think it would be sufficiently destroyed (ie you think in 20 years there would still be holds of bandits or farmers trying to eek out a living and building communities over), how much more should I delay the game? 100 years?