没人能越过芬兰线（No one crosses the finnish line）

As non-aligned  芬兰, survive the  苏联 until September 19th 1944 without losing control of a single core ever.

Despite the description, you are not required to be at war with the  苏联 to get the achievement. You can force them to give up by taking Leningrad, or defeat them entirely, and then wait at peace until the required date.

This is the key to an alternative luck-based strategy, where you simply wait till 1944. Since you don't need to go to war with the  Soviets, you can sometimes completely avoid it through the pure luck of non-historical AI focuses. It is advised to set  德国 to historical so that they may go in on the Soviets and kill them off before they can complete their focus and pray that it works.

「Strategy」

Can be combined with 独狼（Lone Wolf） quite nicely. Go historical.

Start with Finnish Neutrality and then move into doing industry focuses. Get all of the ones that give easy 民用工厂, the Bank of Åland buff, and the cheaper 军用工厂 focuses. Build a 补给中心 on the border with the  Soviets, in the middle of Salla, near East Karelia, after clicking the supply hub construction bonus decision. This is important as you will not have good supply in that region otherwise. Build a line of level 1 陆上堡垒 across your whole border with the  苏联. While the forts themselves won't do much, Engineer Companies give you a 25% defense bonus if fighting in a province with a fort. Queue up 1 基础设施 in Vaasa and 1 in Kymi. This will get you more 民用工厂 from a focus later on.

As soon as you finish your first focus, hire the 白色自由派 advisor from it. While we will aim to have them as a leader later, losing them as an advisor, their buff is so strong and they cost so little that it is still mathematically worth it to hire them. For your next hirings, grab the 沉默的实干家 and the 陆军总司令 who specializes in Army Defense (Genius). When your first leader's public trust falls under -60%, take the decision to have a Vote of No Confidence. Your new leader's public trust drops under different conditions, so while they are in charge, Ban 民主主义. After doing so, you might need to run an Anti-Fascist Raid to get 法西斯主义 under 20% (but don't let it fall under 10%). This leader's buff provides a discount to law changes, so use this time to move up to 部分动员. Queue up a 民用工厂 or two and then start to spam 军用工厂. After this second leader also falls under -60% public trust, vote them out as well.

Now you have Ryti in charge. Ban 法西斯主义 immediately. Complete the 政治统一 focus and then assign the Nationalist Lutheran Priest. He gives you +200 Weekly Manpower (well over a 100% raw increase). His 法西斯主义 support buff is completely countered by our ban, which allows us to "safely" have him as an advisor anyway. Grab all the focuses now in the political side of the tree that give buffs to Public Trust (except Collaboration with the Left) and take the Entice the Masses decision as soon as you can. This decision will come back in a year and taking it a second time usually pushes you into the highest level of Public Trust, which gives a recruitable population bonus and the OP National Spirit Sisu. Use your last open advisor slot to grab the Agrarian Nationalist, as his industry buffs are incredible. You can replace the 沉默的实干家 now and fill out the rest of the Military High Command with your personal picks.

From here, most focuses left are good, though you probably shouldn't waste time on the naval or aerial trees because you simply don't have enough time or production to make use of them. However, aim to grab the 回收与改造 focus either before the war starts or within a couple of months, or your industry will struggle greatly to keep up. The Equipment Capture Ratio Factor boost from this focus is so strong that after finishing it, go ahead and move almost all of your factories producing Infantry Equipment to something else as long as you are at war. You don't need to waste 生产 on guns after this because the  苏联 troops are bringing you theirs for free. Lastly, as mentioned before, once you research Construction III, grab Found Pohjolan Voima to get 5 民用工厂 from just one 70 day focus.

Create an Intelligence Agency, perform any five upgrades to get your second spy, and start working on a collaboration government on the  苏联. You should aim to have 90% collab in order to easily capitulate them. You can either do this starting as early as 1937 or wait as late as 1942 - it's up to you.

As you will only have around 150k manpower, you should use 10-widths with four 步兵 battalions and a 中型自行防空炮 line battalion (take the 自行火炮支援 subdoctrine later to improve it), because  苏联 air superiority and close-air support will be a menace. For the SPAA design, just use an Inter-War Medium Tank's default setup except change to a Medium One Man Turret, Basic Anti-Air Gun, a Diesel Engine (you don't need the speed), and the role of Anti-Air. This design works well for the entire playthrough, and you don't need to research a single tank technology except Inter-War Tank Development (note that Towed Anti-Air is required as well to have access to that gun). It's worth mentioning that static anti-air buildings can also help combat for the skies and keep the enemy wasting time building planes, but they are quite a large construction expense. If you don't get them though, you will definitely need both Dispersed Industry and Armored Trains (and probably to put 5 full factories on them for a while) because the  Soviets will switch to Logistics Strikes after they realize they aren't winning. If you went Concentrated Industry or don't want to bother with the Armored Trains, just max out at least one province worth of static anti-air buildings in each air sector.

For support companies, it's hard to go wrong, but it is worth mentioning that both unique Finnish support companies (冬季后勤和Long-Range Patrol) are very good and also on the cheap side in terms of 生产花费. 冬季后勤 is a unique company with extreme Snow bonuses and very high Defense, while Long-Range Patrol is just a strictly better version of the 骑兵侦察分队 (it even benefits from the Recon technologies). You can go for Mountaineer and/or Ranger technology in order to get access to the 侦察游骑兵连 support company, which gives really good defense bonuses after you've improved it by taking the relevant Special Forces doctrines. However, I just stuck with 工兵连, Long-Range Patrol, 冬季后勤, 支援火炮连, and 支援防空连.

You can easily get around 20 of the aforementioned 10-width divisions. They usually average from 700-1k defense if you've stacked all your bonuses right (Sisu, all support companies, defense advisor, infantry advisor). Train them to level 3, and be ready BEFORE mid-September 1939. The  Soviets should have very little supply (the AI doesn't know how to handle this), and their divisions should be equally bad + purge debuffs. Even then, the first couple of months in particular will be dicey and you should probably reduce game speed a bit to keep a closer eye on everything and micro your units.

As soon as the war starts, switch your Conscription law up to at least 大规模征兵 and trigger the Balance of Power decision now available called Appeal to the Finnish Spirit (if you want to min-max it, watch your manpower's mobilization status and switch up to a higher Conscription Law every time you reach the limit and then run out of Manpower). Don't forget to grab the 拼死防御 subdoctrine, as this makes a huge difference. Make sure to queue up divisions for training immediately because you will need them as soon as possible. Also, Aland is demilitarized until the war starts, so it doesn't hurt to queue up 2 海岸堡垒 and 1 陆上堡垒 on Aland as soon as the war starts and the restriction is lifted. This will let you breathe a little easier when garrisoning it.

In the initial push, you will probably need everyone on the front lines, so use your first set of newly trained reinforcements to shore up any weaknesses. Send everyone left from that batch to garrison your ports. Start with Aland because you instantly lose if they invade there without a unit on it. Do not hesitate to force-deploy the above 10-widths at 20% training or spam your 指挥点数 on Last Stand. Also, don't be afraid to shuffle troops around on your front line, even if it creates a temporary gap. The AI is not eager to rush the gaps as long as they are not more than 1 tile wide because of how poor the supply is in the area (and because they expect you to pin them to prevent the movement), so shuffling a unit over a tile to shore up a bad battle is absolutely worth it. Particularly vulnerable areas are both plains tiles in Petsamo (north) and the two border tiles in the south next to Leningrad. I ended up needing 3-4 units on the two weakest tiles in Petsamo (the port itself and its adjacent Marsh) and 5-6 units on the two weak tiles up against Leningrad, so I made a tiny Fallback line in each place and assigned 2 less units than I needed to hold the area (so that when the 2 units automatically placed there from the front line joined in, it was just enough). Note that if you lose individual tiles here and there, it is not a violation of the achievement. You must lose the majority of the state to fail. Thus, if the two tiles next to Leningrad fall, you can fall back 1 tile away from the city. You begin the game with level 2 forts on those tiles anyway, which provides a nice buffer.

As the war goes on, the  Soviets will attempt to naval invade you an increasingly large amount. Make sure you've garrisoned all 6 ports with at least 1 unit and have a couple extra ones that can shuffle around to beat back invasions. Be especially careful about Aland, which will be hard to reinforce due to  苏联 convoy raiding subs. You may need to Last Stand against naval invasions there on rare occasion. You will want to garrison the ports because you don't have enough units to cover the entire coastline (obviously), but you are still technically vulnerable in some states with a lot of coastline like Uusimaa. They can also naval invade Petsamo, which is one of their more dangerous tricks, since they'll probably be hitting that tile with 12 units simultaneously (3 from both adjacent tiles and a 6 unit naval invasion).

Because you are no longer limited by your manpower (high Conscription law + 拼死防御 + many focus buffs) or Infantry Equipment (thanks for the guns,  Soviets), the easiest way to prepare for offense is to duplicate your Infantry template and save the new one under a different name and icon. Keep your port garrison troops on the older template but switch your front line over to the new one. Now slowly add additional Infantry units to the new front line template one by one as your resources permit, until you reach your preferred offensive combat width size (I went with 18 on a whim). When you're ready to push, replace the 工兵连 with a 野战医院 (to conserve manpower) or a 后勤连 (to help with bad supply areas). You can also add SPGs if you prefer. I would not recommend Line Artillery unless you plan to switch out of 自行火炮支援 and grab 火力集中, as Line Artillery aren't worth using much until they have that combat width reduction. From here, just wait for the  Germans to join the war (or do it yourself if you're feeling frisky). The collab government + them getting exhausted by you will allow you to cap them by mid-1942. Once capped, just leave the game running till 1944. And that's it!

In order to get 独狼（Lone Wolf） as well, make sure you take all the states required that are being held by the  Soviets in the peace conference. Beyond those states, you should puppet as much of the  苏联 as you can. Justify a war goal on Germany's Norwegian puppet,  Reichskommissariat Norwegen.

It is tricky to simultaneously new holdings, maintain an offensive army for pushing into Norway, and maintain strict defensive lines and garrison your ports with the limited manpower you will still have for a while. So if you're low on manpower, switch your garrisons over to Inter-War Light Tanks (make them as cheap as possible with a Close Support Gun). This uses less manpower and also minimizes your losses (hardness of tanks prevents rebels from doing most garrison damage). Max out the number of 轻型坦克 in the division template for the garrison to get back even more manpower (this is a weird quirk of garrison behavior where larger templates are almost always better). Inter-War Armored Cars work just as well if you prefer those. You can start making these before your war with the  Soviets ends to build up a big stockpile of them in advance.

Declare war on  Reichskommissariat Norwegen. You can choose to call your puppet into the war in order to take some pressure off, but it's not necessary. You can also use their manpower to make units if needed. If you want, you can simply let the AI take everything you took from the Soviets and fall back to the Winter War defensive lines you used for all those years, with the same templates you used back then (just be very careful you don't give away any of your original states here, if you didn't wait until 1944 to do this). The  Germans are even worse at attempting to break through than the  Soviets, so you shouldn't have any new issues.

You can accept all the 同盟国' non-aggression pacts but make sure you do not give  挪威 Military Access. If the 同盟国 take any of Norway and restore their government in exile,  挪威's original cores will not be part of the peace deal (to fix this, you would need to fight the 同盟国 afterwards, which is possible but sucks - this strategy is attempting to avoid that).

After capitulating the puppet, justify a war goal on  瑞典 for your core state of Norrbotten. When you declare on  瑞典, they should join the 轴心国 because you are their enemy and at war with the 轴心国 already. Now, both remaining cores you need are technically part of the 轴心国 and even part of the same war. Beat back  瑞典, and at this point, you've won. Just help the 同盟国 capitulate the 轴心国 on whatever front you like. When the peace conference fires, just take Finnmark from  Reichskommissariat Norwegen and Norrbotten from  瑞典.

Alternative Strategy (Patch 1.16.9)

Possibly due to a bug, the AI Soviet Union will not start the Winter War if they have a non-aggression pact with you at the time it finishes the requisite focus, and it will not start the war later, when the non-aggression pact can be cancelled, either. So:

• 以历史模式游玩。
• Create an intelligence agency.
• In late 1938, start doing relations improvement + diplomatic pressure on the  苏联.
• In January or February 1939, request a non-aggression pact. Put an army on the border, to make it harder for them to break off the pact later.
• They do the focus, you get a demand for Karjala, you refuse, they get a war goal against you, on which they can't act.
• Now you just sit and wait. (You can even do the focus for the Continuation War and you'll be invited to come along when the  德意志国 attacks the  苏联 in 1941. It's risky - you might lose some states this way - but it's more fun than sitting and waiting until 1944.)