Let's say I want to conquer hillocks with 200 population that was taken over by goblins. Lets assume the military has full default sets (metal or leather), and has been doing basic training for last year, but no "one man army master swordsman vampires" are on board. Do I actually need about 200 military dwarves ? Or more like 100? Or maybe with full equip 2 x 10 melee and 2 x 10 range squads would do? What if I want to conquer 200 population dark pits of cheekclaps? And how does one conquer sites that have populations counted in hundreds or thousands?
The current version of DF isn't designed for you to be able to conquer the world. You can still do it if you're very patient, but be aware that you're going against what Toady designed the game to do.
I've run a lot of missions, and these are my best guesses on how the mission combat works:
1.
Leadership is key, meaning the Military Tactics skill, possibly combined with the Organizer skill. At the beginning of the pillage or raze mission, your leader's skill is compared to the defending leader's skill. The result establishes a multiplier that usually covers the rest of the battle. This is reflected in the report's paragraph about "unrolled a plan" and "positional advantage".
The defending leader seems to be the historical figure at the site with the highest skill. A big city will have lots of historical figures, and thus a high chance of a defending leader with high skill. Small settlements often have no historical figures and thus no leaders, so your attackers automatically get the highest tactical multiplier. So you might want to send large pillage missions against a site that you haven't pillaged before, to test the leadership. Once the leadership is gone, it's relatively safe to send smaller missions for better XP. But there's always a chance that a historical figure will wander into the site as you're pillaging it, so you can never be certain that a site is leaderless.
If your militia commander's squad is in the mission, then he's always the mission leader. Otherwise, I'm not sure how the leader is selected. A large battle will sometimes have multiple skill checks. While the first check is always with the mission leader, the subsequent checks involve random squad leaders. So you should grind up XP on all your squad leaders. That's why the best approach for missions involves dozens or hundreds of single-squad pillage missions against weak targets. Raze missions waste potential XP by killing defenseless civilians too quickly. Pillage missions kill 10% of the population, so you can get 15 to 20 missions---at 500XP per mission for the squad leader---before the site is empty.
2.
Non-humanoids are Super-Effective. In an earlier version, every animal at the site would fight in its defense. So the only way to attack elven sites with their giant animals was to first send raid missions to steal the animals. Now that has changed. Most domestic animals won't fight to defend the site. Some types of animals will still fight, and I haven't figured out which ones. If you're worried about the animals fighting, you can always steal them first.
Trolls and ogres are ultra-dangerous, presumably because the one-on-one mission combat uses body size. And you can't steal them because they don't count as livestock.
3.
In-Game Site Info is Garbage. The only reliable way to know what you're facing in a site is to export legends. Even then, the situation could change while your soldiers are en route. A competent leader might arrive to defend the site. Or, with a weak site, another civ could conquer the site just before your soldiers arrive. Since the game doesn't check changes in site ownership after mission creation (Bug 11557), you can accidentally start a war with a peaceful neighbor.
4.
Skill and Equipment. The formula used in mission combat is very, very different from what you see in a fortress. Soldiers who fight on missions only gain XP in two or three combat skills, though I can't find my notes on which ones. IIRC, it's mostly weapon skill. You could export pre and post data from Therapist into a spreadsheet to get a clearer picture.
I doubt that equipment affects mission outcome in any way. The only equipment mentioned in the reports is the weapon being wielded. And that might be drawn from the highest weapon skill rather than the actual object in the soldier's hand. I've never tested it.
5.
On Large Armies. Even if you have high-skill dwarves with brilliant leaders, there's a practical limit on the sites that you can safely attack with missions.
First, there are no real hit-and-run missions. The difference between pillage and raze is simply how much of the civilian population you'll kill
after you win the battle. I think the battles themselves are identical. So there's no way to whittle a site down. If a city has 300 people in it, then you're gonna need at least 400 soldiers to attack it, just as in real life.
Second, the important mission combat is presented as duels between individuals. If Dastot is fighting an ogre, it's not clear how much help he's getting from his comrades. There's no way for your dwarves to rush the ogre en masse, as you can in fortress mode.
Third, it's important to think about how the soldiers leave your fortress and return. When you send a mission, each squad marches to the map edge tile closest to the squad leader. It's a fairly efficient process. But when the soldiers return from the mission, they hold what I call a Victory Parade: They return one dwarf at a time, just like migrants. That's not a big deal if you sent 20 or 30 dwarves. But if you sent 120, you'll be watching that parade for weeks. And if the parade is still going on at season change, then there's a chance that your returning soldiers will march into a besieging army.
This is why missions work best with small embarks. If you try running dozens and dozens of missions on a large embark, then your soldiers will spend a lot of time walking back and forth. The next fort that I use for missions will definitely be 1x1.
6.
Adventurers. Missions are best at stealing items, settling sites, and exterminating helpless civilian populations. But they suffer from a definite upper limit. You can't run a thousand-man fort, which means that you can't field a thousand-man army.
Adventurers don't have those limitations. In fortress mode, you can give adventurers military training and excellent gear. Then release a party of two or three of them on the world, and they can kill anything. It doesn't feel particularly heroic to massacre helpless human monks or elven herbalists by the dozens, but it's very effective in reducing site populations. The only limit is your patience. Once you've cut a site down to size, you can switch back to fortress mode to finish it off and settle it. And that leads to unretirement, which is a massive headache unto itself.
