I had the exact opposite with respect to liaison vs. caravan, which served me fine: all contacts with the dwarven civ had failed for four years straight, three times because of sieges, once because the liaison spawned into the middle of a kobold ambush and the caravan got scared of chained prisoners and ran away.
This year, the liaison got in alive, finally raised us to duchy and got a new population account - i had reduced pop cap to 100, and that still didn't help - the last visit had apparently been before we even reached 100, and we'd been at 210 by now. So i lowered the cap all the way to ten, to finally get rid of the ultra-annoying trader fake migrants who just keep clogging spawn points and get themselves killed in the most stupid fashion possible. This time, the finally got moving when the caravan entered the map, which wasn't such a great choice, because by then i'd activated the bridge trap and the morons went right in.
And what really, really annoyed me was that this apparently counted against the loss-of-life rule for caravans, i.e. they promptly refused to trade. Good thing i had no magma available, i'd have torched them without a second thought.
Oh right, some goblins with trolls showed up, got themselves crushed, end of story. And there was another kobold ambush in winter, nothing some bridges couldn't handle. I've dug a tunnel network that might _hopefully_ help to get diplomats inside alive and made a small aquifer trench for a water power plant giving 1000 energy. I'm using two areas where the aquifer is at different z-levels, using the natural flow from the higher infinite source to the lower infinite drain. Works without a hitch and feels a bit less cheaty than zero-point or perpetual-motion-via-pump generators.
No fortress deaths this year apart from a watchdog (gotta improve the tunnel design, ambushes will apparently path straight to reachable creatures over paths into the fort), dead invaders are a bit over 500 now. Imported wealth keeps dropping ever since i stopped migration, and i reduced it even more by melting down the weapons and armour of the two sieges that required use of the spike corridor. 80k imported, a bit over 300k exported wealth, with a bit over 9M nominal fort wealth after nine years.