I think it'd be more fun if goblins were more of a challenge. I'm sure there is a way to make it so certain species tend to be at war with each other. Let's face it: in history gen, it's a lot more interesting when there are lots of wars going on between different factions.
So, let's recap the things that affect politics:
* The density of opposing start groups. All species have reasons to go to war with each other it seems, except the same species; I've had 2 seperate dwarf civs live side by side forever with no troubles. Goblins babysnatch from other goblins though so I'm not sure what that's all about. (In one map I had one poor infant abducted 3 times in the span of 3 years).
* Ethics seem to have a large in-game effect, either on trading in fortress mode, what they do to you in adventurer mode, or how they react in history mode.
* Religion seems to play a major part in starting wars; opposing spheres give a pretty consistent reason for declaring it, ie. "the war started over the worship of rivers" or whatnot.
* TREE_CAP_DIPLOMACY: Obviously the elves declare war on you for this, but it does not affect history mode.
* The civ entity biomes let the civ spread to wider areas (humans spread so rapidly because they can use a wide variety, for example). Letting many civs spread to many areas may let them come into conflict more often.
Some things that might affect politics:
* BENIGN or EVIL tokens: do these affect politics at all? Maybe this makes it less likely for a civ to be at war with the same token, or accept/reject offers of peace.
* TOLERATES_SITE: do the site tokens affect politics at all? Maybe a civ is more likely to go to war if they have somewhere nearby they can conquer.
* The goblins have the tag [ABUSE_BODIES], I am fairly sure this allows them to put heads on pikes and hang corpses and so on after they win an attack. Maybe this also is affected by the ETHIC token MAKE_TROPHY_SAPIENT?
Now, so far I've had the most success in making a richly historical world by: very carefully adding enough max civs to the entity list and the world_gen tokens so that I don't get infinite rejects, so that the civs are nice and clustered together. This almost always ensures some good conflicts. If the civs expand to their max size and aren't overlapping any enemy forts they tend to stagnate for the rest of history.
Ethics are a pretty big deal I've think, too. I set most things on goblins to ACCEPTABLE (ie. slavery, eat_sapient_other), and it gives people a lot of reasons to go to war with them. Unfortunately this also means my goblins are usually vastly outnumbered; I have yet to try boosting their default site numbers, maybe that'd help.
I think the easiest way to make civs specifically at war is to change their religions to directly conflict with each other. Has anyone else found any better ways?