Realms started to survive more wars as the player base shrunk. People could no longer afford to set up colonies to replace existing realms. With the game stuck at 400 players, I doubt people want to destroy any realm but they probably still want to take at least a city or few regions.
Yes, I'll agree that realm survival increased with time.
The feasability in colonies is one factor, but there was also a culture shift, fed by a specific "anti-destruction" movement on the d-list and then forum and an increasing individualism and anti-coalition sentiment that encouraged realms to go on their own paths instead of following their bloc all the time.
