In one of my large sized cities, I have reached a population of about 800,000.

But about a year (in game time) after that, the population drops down to 200,000.

I've tried everything that I could to stop this. I have also yet to find any reason for this to be happening. I have even tried to play through it but that does not show any signs of success.

If you have any ideas or similar experience with SC4 that is similar to this, please write about it here.