When in combat, do players that are defending a zone (assuming that there are units in the zone) have the choice of defending or just letting the opponent

apply damage to the capital? Do the units have the defend?

Thanks in advanced...

Sorry for the type o's...

Do the defenders have to defend their zone being attacked? Or can they choose not to go in battle?

On p.12 under "Declare Defenders", it says the defender now declares defenders (if any) which will participate in the battle.

So, I would say no, units in a zone do not have to defend if you so chose.