Definitely build up. Another thing that's very useful is to train up the maximum number of ninjas and monks and keep using them to destabilize neighbors, etc. You can afford lots of agent missions while trade is still good before RD.

Sabotaging enemy armies and assassinating their top ranked generals can give you breathers for the dog piles. It's also much harder for the AI to make war on you effectively when all their farms are in ruins and they're constantly wracked by rebellions.