Same problems really. Once people start breaking alliances, I feel compelled to crush them to set an example. (not that it does)
And then I end up somewhere around turn 40-60 and bored to death as I control turncount*1.2 provinces and only micromanage my (vast) empire and consider starting a new game.

It seems that the AI can't handle an expanding human player. But sitting back and just managing 2-3 provinces isn't really my thing as this isn't Total Sit-at-home but Total war.