Raids on caravans would be interesting, and would open up jobs for guards. I am, as youi have probably noticed, stating the obvious. But shhould the guards just beat the raiders off individually, or will they act in coordination? I doubt it will matter either way for a simple raid, but I myself prefer strategy and tactics. But what will the raiders do with the loot, if they are NPCs? Just make it vanish? Will players be allowed to raid caravans? In guild wars, the answer is yes. Otherwise, probably not, and needs discussion in the PvP forum.
As for raids on cities, should they be simple raids, or full-scale sieges? Should a player suddenly take command of the city forces and defeat theh invaders, or will masses of players swarm out of the cities as an undisciplined mob, only to be mowed down by arrows and slashed down by some passing cavalry? Also, should thhere be traitors in the city, who will open the gates to the invaders and cause grief to the inhabitants? I think thehre should be, for realisticism. As for players taking command of cities... Perhaps if the \'guild dominance\' is strong enough, the guild becomes responsible for the defense and welfare of the city. I could go on and on about my idea of guild dominance in cities, but this post is too long already.