Total War: THREE KINGDOMS

Thanks to https://steamcommunity.com/app/779340/discussions/0/29627693... for the Records tip. The guide doesn't do more than go over the very broad strokes, so I'm going to try to do a more in-depth process. The writer says they got it in 15 turns, I got it in 27. There's definitely some stuff I could have cut out, but I don't think I could do it in less than 20 (maybe somebody will find something I missed in my run).

Major Points:

• Switch to Records mode, which seems to remove a lot if not all of the story events, including Lu Bu killing Dong Zhuo
• Play Ma Teng, who starts next door to and at peace with Dong Zhuo.
• Capture Chang'an and by extension the emperor ASAP. This will give you vassalage over the Han Empire and will be a large source of prestige. The more Han Empire territory you can save, the more prestige you will get.
• Prioritize upgrading settlements and building administration offices for gradual increases of prestige.
• Don't make Lu Bu's army withdraw from the map. You're guaranteed to get him as a general during annexation if you have an army slot, but not when he's waiting around in court.

In-depth Turn Guide

Turn 1:
Follow the story and capture Wudu, Xiabian. I converted the workshop so that building the inn will be a little cheaper. Also use Hua Lanli's building assignment here to decrease costs and build times further. When the turn ends, sometimes Gong Du will start sieging the city (about 50/50 chance that happens for me). You can definitely fight him off, but battles in Records mode seems to be harder than in Romance, both in auto-resolve weighting and in the actual tactical combat (I suspect it mostly has to do with how Records mode reworks fatigue). You may want to restart unless you're sure you can beat him without taking too many casualties.

Turn 2:
I built an inn next to get some more gold. Start moving towards the remaining Wudu county.

Turn 3:
Capture the last Wudu county. This will protect your back as well as add to your economy. Start upgrading your settlement level.

Turn 4:
Move towards Chang'an (Possible paths below the next turn). I think Fu Gan, a strategist, becomes a usable character at this time, so recruit him and at least one trebuchet into your army. Feel free to round out the rest of your roster as well. If I'm wrong about Fu Gan, recruit another strategist instead. I think Ma Teng should have leveled up at this point, so use the point on the green skill that grants increased replenishment.

Turn 5+:
Alternate between upgrading the settlement and building administration offices for prestige, whatever you can afford. You should be able to reach second marquis around turn 10-ish on territory upgrades alone. At this point, we're going to start working towards Chang'an. Spend another turn or two to reinforce your troops if you need to. We have two paths we can take towards our goal.

Path A - South through Hanzhong: The one I went with in my final run was through Hanzhong and across the mountains between Meixian and Lantian. This is a straighter shot to Chang'an, and seems to be the shorter of the two routes. However, Gong Du might have killed Zhang Lu and taken Hanzhong. If he did, he will most likely also bolstered his own forces. Not impossible to dislodge, but definitely annoying. Save 25% movement points when you're going in to put your army into ambush stance, otherwise Gong Du seems to notice you coming and will reinforce Hanzhong, making it even more difficult if not impossible to take. From the border between Hanzhong and Wudu, it seems to always take two turns to reach the city even with max movement, so you're not losing anything from hiding yourself midway. Gong Du will most likely attack after you take Hanzhong, but you should be able to fight him off. If Gong Du has anymore territory near you, feel free to knock them out to keep your back covered. Otherwise, spend some turns to replenish and march on Chang'an. If Zhang Lu is still alive, the process is pretty much the same, maybe easier as you start at peace with Zhang Lu, so you can trespass on his lands before taking his capital (the same way we're going to take Chang'an). Alternatively you can sign a military access deal with him and just ignore all that altogether (you might want the city for prestige, though).

Path B - North through San Pass: It's seems a little bit longer than the South pass, and you'll be trespassing on Dong Zhuo's land for a while. Normally you also can't pass through spheres of influence by territories or armies not allied to you. However, while in Path A my normal movement seemed to be blocked by Meixian, my forced march movement was not (might be some rule I'm forgetting). You might be able to pass by San Pass the same way. Otherwise, you'll have to capture it and the next county over before Chang'an, thus declaring war on Dong Zhuo and giving him notice and time to prepare for your assault. You might also have to contend with Lu Bu. Still, most of Dong Zhuo's deployed armies including Lu Bu's will probably be occupied by other matters, and he won't be able to raise new ones fast enough to be any threat to you at this point, compared to Gong Du who does have one army that just keeps getting stronger if you let him.

Turn 10+:
If you haven't already, you should be able to break your treaty with Dong Zhuo without generating treachery around this point. Treachery may affect his opinion of you, which may or may not affect his willingness to agree to peace/vassalage. To be safe, I waited and didn't risk the treachery penalty.

Turn 14+:
Your army should have reached Chang'an around now. Chang'an is probably a level 5 settlement with a level 2-3 garrison. Auto-resolve probably calculates a loss on this one. I've tried manually fighting the battle several times, all ended in failure. If you can manually win the battle, do so. Otherwise, you might need to siege it down a couple of turns first.

Turn 16+:
This was the point I was able to auto-resolve capturing the city (they tried to drive me out first at least once before this, which I was also able to auto-resolve). After going through a lot of pop-ups, you should finally be able to rank up to Marquis. If you're still short, capture some more cities from Dong Zhuo. If you can vassalize Dong Zhuo at this point, do so. For me, Dong Zhuo was still being stubborn, so I had to fight another turn or two first. If possible, DON'T make Lu Bu's army withdraw/undeploy/whatever the term is. If he is deployed as a general and you have a free army slot, you're guaranteed to get him in the annexation, whereas, if he's waiting in court, there's a chance he will leave instead.

Turn 20+:
This was the point I was finally able to annex Dong Zhuo, yours may be earlier. Assign Dong Zhuo as administrator of a city (DON'T make him administrator of a gate, you can't grant independence to gate commanders). Raise Lu Bu and any other generals you want in his commandery. Grant him independence, then immediately declare war on him. Skip a turn to let Dong Zhuo deploy himself, then attack him with Lu Bu. You can auto-resolve the battle if you want, the achievement will still unlock.

All in all, still lengthy and kind of a pain, but at least it's a surefire way at both of them without getting DLC.

Edit: forgot to mention that you should also get Guangdong Coalition at the same time.