In a couple of games I'm allied with Rome and I find that when Rome is attacked, or when Rome attacks, and I thus become engaged in a war I can essentially ignore it. I get all the benefits of peace with Rome and have Rome acting as a nice buffer between me and a number of troublesome neighbours, but I don't have any (or very little) downside. I don't have to send armies to attack the enemy states, I don't even have to send armies to help defend Rome, I just carry on doing my thing...

Now this is great for me, but I'm wondering is this realistic? If I was Rome I'd be expecting my allies to send some armies to help fight the enemy, or send armies to defend borders while the legions do their stuff, or even send money to help the war effort. If I had an ally that did nothing then soon they'd not be an ally, but the AI seems happy to let me continue doing nothing to help.
I'm wondering if the alliance should be reviewed periodically based on the help given. The sort of factors, that would score well would be;
* each army actively fighting a common enemy... with more score for battles won
* each army on the border of a common enemy... with more score for repelling enemy raids or attacks
* Donations of gold
* Donations of units
* etc.
If the obligations of being an ally are not fulfilled then the alliance would be dissolved. Perhaps the ally should issue some comments over time to give a hint that more is expected of an ally before dissolving the arrangement.
Anyone else seeing this? Any thoughts how alliances could be improved?