Terra Mariana
An achievement so hard to get that only 0.6 of players have done it.
I did it. It aint much, but I did it after many many retries.
If you're still interested then here's how I did it. I went into this knowing it would be tough, but I had no idea. The one good thing about this achievement is that the start is fairly simple.
1. Rival the Livonian Order. The order will get one or two allies. Scotland and the Teutonic Order. In my many, many attempts, Scotland only allied the Livonian Order a few times, but even when it did, they never helped out in a war.
2. Improve relations with Muscovy & Denmark. Denmark tends to be against allying you, but something seems to happen at about 110 relations and they can be allied. About 3/10 runs they still refused to ally you. If that doesn't happen, it's not the end of the world, but it's pretty useful if they do.
3. Denmark will go to war with the Livonian order by 1448. It can be really tempting to dow them now, but don't. The Teutonic Order start with a great general and even building up to force limit they will stack wipe you. I've played with mercs and going over force limit and I could not beat both Orders. Instead the best option is to wait for the Teutons to be unwilling to support the Livonians in another war. Focus on carpet sieging. If you're luck you can take all the Livonian Order. It will set you back in adm and cause an unhealthy amount of AE, but you have to do it. Times I haven't done this the territory I've left has been taken by Lithuania/Poland/Muscovy. The worst case would be Muscovy as you need them as an ally.
4. Moment you peace out, ally Demark. In most runs Denmark will take a moment to update and understand that we now hold provinces they want. Before that happens they are almost always willing to ally. Ally them. Denmark will dow you within months if you don't. The alliance will break almost immediately, but the truce will give you much needed breathing room.
5. Muscovy still won't ally you so rival Novgorod. This is impossible without at least most of the Livonian Order territory. Avoid taking territory from Novgorod, you want to keep Muscovy happy. If you don't the Lithuanians/Commonwealth will attack you. Hell Poland + Lithuania at this point are much stronger than Muscovy that most of the time even if you do ally Muscovy and they attack you, you will lose.
6. I've yet to determine if this a run breaker, but good runs tend to be highly dependent of Poland's decision to PU Lithuania. I got incredibly lucky and Poland choose not to PU Lithuania. This led to me and Muscovy being able to beat Lithuania and take some territory.
7. Around this time The Teutons will get the Danzig or War event Danzig will get released, war between Poland & Teutons will happen. Weird things happen at this point. Danzig starts out just prior to the war allied & guaranteed by Poland. During the war they lose the guarantee and Poland in my run didn't want to help. I took some territory from them, but I couldn't annex them outright. AE rears its ugly head.
At this point you should be in a position to slowly expand and exploit times of weakness. I finished the above by around 1470. I then didn't do anything for about 100 years. Poland & Lithuania allied and remained pretty good ones, which was a pain as all the territory I wanted, they now held. Denmark dow'd me twice during that time and both times I was able to beat them, the last time forcing them to renounce their claims. Sweden...oh poor Sweden. I know they look strong now, but that's a recent thing. That was the end of their 6th War of Independence! During their many wars, I took Gotland from Sweden. I probably played it too safe for a while, but I was terrified at that the thought of losing my progress at this point. It didn't help that Muscovy didn't once want to join me in an offensive war. It wasn't until they formed Russia they choose to help me. Not that I think they were selfish, more that for about 100 years they were 7k in debt. My war against Lithuania went great. The island of Osel is a perfect trap if you have naval superiority. The AI loves marching an army to Reval via Osel and getting their whole army caught.
You're going to have to play fast and fickle with allies outside of Muscovy/Russia. At times I was able to ally Poland to defeat Denmark and then Denmark to defeat Lithuania. Muscovy/Russia can't always be there for you and you will need an ally. Early on tried to get into the HRE and managed to ally Austria, but by the point I got Danzig I was already too high in Development to get in. In between wars you'll want to dev up. My dev is only 480, but I would guess at least 150 of that is from deving up. My choice of ideas reflect this. Even with less dev than Poland I had more armies. Another part of that was Baltic Trade node. It's not the best in the game, but it's pretty damn good. My early wars gave me control of a lot of the high trade value provinces, so my income was pretty high early on.
This biggest set back to this run was the League War. I got dragged into it fresh out of war with Poland and Lithuania. This war was disastrous and the outcome continues to be. Not only did the Catholics lose the war the HRE has been crippled by it even almost a hundred years later. Most of the HRE wasn't protestant, they were reformed, but the war ended with protestant victory. Even not much of the HRE are still reformed. This led my best hope for an ally in Germany, Austria, getting neutered and Poland by itself having more than enough manpower to take on the the weak emperor. It's gotten to the point that if I carry on I'm tempted to get the religion idea group and just eat all of Germany. I don't think the HRE could stop me.
I'm not sure what I'll do now. Riga is pretty much an emerging power. I could take Poland or Lithuania without too much issue, or many I could try for India and build a colonial empire. Idk. This achievement was very difficult, but I would recommend it for people who want to learn the diplomacy/dev game.