Just sounds Damn Unlucky!! You get massive Moral Hits when Your general Dies and if he had some Bad Vices (Good runner, Indecicive, sybarite that kind of thing) that lower your troops Moral It only takes his death to rout a low valour unit which then means the penalty from them routing on nearby units can set them off starting a chain reaction rout of your entire army! (Put low valour units out towards your flanks to minimalise the effect of this)

Thats why you should always try and have a few elite units who wont be affected by neigbouring routers to hold your line together.

Moral can be quite a complex issue in TW games but once you master it it become quite easy to keep all you chaps on the field even in some quite dire situations.

Also goes without saying now, dont put your General next to cannons!